In this Leaf Score series on crib mattresses I’ve already looked at the troublesome chemicals and materials used in the majority of mattresses for infants and toddlers. These include polyurethane foam, polyester, and polyvinyl chloride (PVC). So, if you’re trying to avoid these materials in a crib mattress, what are your options for more eco-friendly, non-toxic crib mattress materials?
Importantly, some of the best materials for a crib mattress differ from those I’d recommend for an adult mattress. While crib mattresses may seem overly firm by adult standards, a firm sleep surface is essential for sleep safety for infants. Too soft a surface and an infant may struggle to maintain a clear airway. This means that one of my favorite mattress materials, kapok, is a no-go for crib mattresses. Kapok is far too soft for a crib mattress surface and should be avoided; you may find kapok in the toddler side of a dual-sided crib mattress, however, so be careful which side faces up if an infant will be sleeping on the mattress.
Indeed, if you’ve been doing your research on mattress materials, you may have come across a Cochrane Review from 1993 which found that the risk of SIDS was greater among infants who slept prone on natural fiber mattresses (odds ratio, 6.6) than among infants who slept prone on other types of mattresses (odds ratio, 1.8). While this sounds bad, the data also showed that a natural fiber mattress was not itself an independent risk factor for SIDS, with no greater risk found in infants sleeping on their back on such mattresses
Also, when you dig into the data, it quickly becomes clear that the natural fiber mattresses included in the review were much softer than the foam mattresses. These mattresses were made with a kapok stuffing or ti-tree filling that compressed considerably and left an indentation, suggesting that an infant sleeping on their side or tummy could quite easily have their airway compromised on such a mattress. These days, natural fiber crib mattresses are much firmer in general and don’t pose the same safety risks. And, as always, infants should be placed to sleep on their back, not on their tummy or side.
One of my top picks for an eco-friendly, non-toxic crib mattress is the Naturepedic Organic Cotton Classic Crib Mattress (View Price on Walmart). Receiving a 5/5 Leaf Score, this waterproof mattress is made with organic cotton, innersprings, and a non-GMO sugar cane derived polyethylene waterproof cover. It is made without harmful chemicals, and contains no latex, soy, GMOs, vinyl/PVC, phthalates, formaldehyde, flame retardants, polyurethane foam, or perfluorinated compounds (PFCs). You can read my full review here.
Now that’s out of the way, let’s look at the kinds of materials available for eco-friendly, non-toxic crib mattresses. Leaving kapok aside, there are plenty of excellent mattress materials that don’t off-gas, have a lower carbon footprint (typically) than synthetic mattresses, and are more easily recycled, or able to break down naturally. Some eco-friendly crib mattress materials to look for include:
- Organic wool
- Organic cotton
- 100 percent natural latex (Dunlop, ideally, not Talalay, which is softer)
- Coconut coir (with caveats)
- Pros and Cons of Wool for Crib Mattresses
- Pros and Cons of Organic Cotton Crib Mattresses
- Pros and Cons of 100 Percent Natural Latex
- Pros and Cons of Hemp Mattresses
- The Pros and Cons of Coconut Coir Crib Mattresses
- Pros and Cons of Innerspring Crib Mattresses
- A word about polyurethane, TPU, and polyethylene
- Plastic waterproofing for crib mattresses
- Alternative mattress cover materials
Pros and Cons of Wool for Crib Mattresses
Wool naturally wicks moisture away from skin and is flame-resistant and antimicrobial, making it an ideal material for a crib mattress. A wool mattress or mattress top can help your baby maintain a comfortable body temperature, keeping them cool in summer and warm and cozy in winter. Wool doesn’t off-gas nasty chemicals, is naturally resistant to mold and mildew and is resistant to dust mites.
Wool is also fairly firm, making it a good fit for a crib mattress as it won’t compress and conform to a baby’s body and create a safety hazard as a softer mattress might. Wool is also naturally water-repellent, assuming it still holds some of its lanolin (an oily substance produced by sheep).
Unfortunately, though, some infants can develop an allergy to lanolin although not usually to wool itself. And, as wool mattress covers are water repellent because of their lanolin content (some even have lanolin added), the risk for a lanolin allergy may be higher than with regular wool. That said, many ‘wool’ allergies are actually thought to be allergies to the chemicals used to process non-organic wool, and you’ll probably use a cotton top sheet over any wool layer anyway, so your baby won’t have any direct contact with wool itself.
Indeed, wool puddle pads are very popular for placing on top of a waterproof mattress and under a cotton cover sheet for added protection. These puddle pads can be quickly removed and hung to dry as needed, with the waterproof mattress cover just needing a quick wipe down to keep it clean. As cotton absorbs moisture and wool wicks it away, it’s a good idea to combine a cotton pad on top of a wool pad to minimize the potential for wetness to penetrate the wool pad. Be sure to check that any wool puddle pads are 100% certified organic wool as some pads contain synthetic fibers.
Bear in mind that while wool is water-repellent, it is not, however, water-resistant. This means that you’ll still want to buy a mattress with a waterproof cover made with food-grade polyethylene, or cover a crib mattress with a waterproof polyethylene cover and use an extra wool puddle pad for protection.
The main downsides of a totally wool crib mattress are the potential expense and the heaviness, with greater resource use than may be necessary. Although it’s nowhere near as environmentally taxing as making a polyurethane foam mattress, wool production does have an impact on the environment and wool that isn’t organic may be produced with chemical pesticide and fertilizer inputs and other chemicals such as bleach. Most mattresses made with wool only use it as a cover layer topped with cotton, with the interior of the mattress made up of cotton batting, innersprings, latex, or other material. This makes for a much lighter and typically cheaper mattress.
One other downside of wool is that it’s not vegan-friendly, although some sources of wool are considerably better in terms of animal welfare. In the US, wool marked with the PureGrow™ label comes from Californian farms that practice sustainable sheep ranching. EcoWool is similar, and both are arguably preferable to New Zealand wool in terms of animal welfare. Wool certified USDA Organic is also a decent option as is any wool product with GOTS certification.
To really up your eco game, look for organic wool that carries the European kfB certificate awarded to products made with wool sourced with minimal animal exploitation. While I typically don’t buy products made with wool, being vegan, I am very likely to look for a cruelty-free wool crib mattress and wool puddle pads when the time comes to kit out a nursery, given the significant benefits of wool over other crib mattress materials.
It’s also important to differentiate a wool mattress or mattress pad from a sheepskin mattress cover. Even if covered by a sheet, soft materials or objects, such as pillows, quilts, comforters, or sheepskins, should not be placed under a sleeping infant. Sheepskins are too soft for infants and could create a suffocation hazard; they should not be used for infants younger than 1 year, as advised by the American Academy of Pediatrics and many other organizations.
Pros and Cons of Organic Cotton Crib Mattresses
Conventionally grown cotton is resource-hungry and involves the use of pesticides and other chemicals that damage the environment and are bad for human health. Given that you can’t wash a crib mattress to get rid of any residues of these pesticides, I’d definitely avoid buying a crib mattress made with conventional cotton.
Rather worryingly, recent groundbreaking research revealed the presence of a variety of pesticides in the brain tissue of fetuses and infants who died of sudden intrauterine unexplained death syndrome (SIUDS) and sudden infant death syndrome (SIDS) (R). The same study noted that some of these organochlorine pesticides, that is α-chlordane, γ-chlordane, heptachlor, p,p-DDE, p,p-DDT, and the two most commonly used organophosphorus pesticides (OPPs), chlorpyrifos and chlorfenvinfos, were found in samples.
These chemicals, which are endocrine disruptors, are able to overcome the placental barrier, reaching the fetus. They can also cross the blood-brain barrier and impact the basal ganglia which controls vital functions. While it’s impossible to say with certainty that these pesticides contributed to the unexplained deaths, the authors strongly recommend that further research is carried out into the possible connection.
Fortunately, we can limit exposure to pesticides by choosing products made with organic cotton that is grown and processed without pesticides, formaldehyde, or other harmful chemicals. Organic cotton is natural, non-toxic, firm, and nowhere near as flammable as petroleum-based foam. Nor does it release toxic fumes if it does somehow catch on fire.
Organic cotton is an excellent option for a crib mattress, with many eco-friendly crib mattresses available with an organic cotton cover over a layer of wool (as a fire barrier), and an innerspring and cotton batting or natural latex interior. Mattresses that contain a lot of cotton tend to be heavier and feel firmer than foam mattresses, but this firmness is a good thing for a crib mattress.
Pros and Cons of 100 Percent Natural Latex
Latex (natural rubber) is a renewable and recyclable resource increasingly used to make eco-friendly crib mattresses. Rubber trees can provide rubber serum for up to 30 years and the resulting latex is firm, bouncy, and durable. Although it isn’t as biodegradable as wool or cotton, natural latex can be recycled for use as underfloor insulation or other fill. And, eventually, it will biodegrade without releasing toxins into the environment, unlike polyurethane foam.
Latex crib mattresses typically use molded latex Dunlop foam, which is chemical-free and slightly firmer than most polyurethane foam mattresses and also firmer than Talalay latex. Latex is particularly good for crib mattresses because it is porous and disperses heat. This porosity quickly becomes a problem, however, if the mattress doesn’t have a waterproof cover.
The good news is that latex is naturally antimicrobial, resists mildew, and doesn’t harbor dust mites. It is also easy to care for as you can wipe down latex with warm soapy water, dab dry with a towel and let it air dry. Still, I’d highly recommend using a waterproof food-grade polyethylene cover for any crib mattress, along with easily removed and replaced wool puddle pads.
Latex crib mattresses are a little more expensive than some other mattresses made with natural materials, with the cost usually dependent on certifications. Relevant certifications include GOLS – the Global Organic Latex Standard – and FairRubber, which indicate that the product is made using certified organic rubber sourced in a sustainable way by workers who are well treated and properly paid.
Latex mattresses can have a rubbery smell at first, so it’s best to air them out for a few days before sleeping on them. This is not a sign that the mattress is off-gassing toxic chemicals, it is simply the natural smell of rubber and will dissipate within a few days.
When looking at mattresses, it’s important to determine if the latex is Dunlop or Talalay. As mentioned, Dunlop tends to be firmer feeling than Talalay which provides excellent soft support and pressure relief for adults but may be too soft for infants.
Some crib mattress manufacturers avoid using latex because of concerns over latex allergies in infants. This is an area where fearmongering appears to trump science, given that there’s no evidence of latex mattress use resulting in latex allergy in infants. While some infants do develop an allergy to latex, this is largely attributed to latex in bottle teats, pacifiers, balloons, nose cleaners, and medical equipment, with no documented cases of an allergy arising from sleeping on a latex mattress (R). Indeed, it is rather unlikely that an infant would even come into contact with latex from a latex mattress as these are typically covered in a layer of wool and cotton ticking and dressed with a waterproof cover and fitted sheets.
In addition, the latex used for medical equipment, pacifiers, gloves, condoms, and so forth is quite different to that used for mattresses. This latex, which is typically stretchy, is cold-dipped and still contains proteins that can trigger allergy. The types of latex found in mattresses undergo significant washing and a flash-heating or vulcanizing process that first eliminates a large amount of the proteins in the latex and then destroys any remaining proteins.
So, an infant seems much more likely to develop a latex allergy from repeated exposure to latex in a healthcare setting or even from using a pacifier, feeding bottles, or handling a party balloon than they are to have issues with a latex mattress. And, unless there’s a family history of latex allergy, or if an infant or caregiver has a known latex allergy and might touch the mattress in its uncovered state, there’s little reason to rule out a latex crib mattress.
Indeed, the only study I could find that looked at real-life exposure to natural latex found that there was no difference in the development of latex allergy in children who slept on a latex mattress compared to those who slept on a non-latex mattress (R). Most other studies look at immune responses when latex is frozen, crushed, ground up, mixed with solvents, and mixed directly with blood. Unless you’ve got some odd plans for your mattress, then, this exposure scenario seems rather unlikely.
Pros and Cons of Hemp Mattresses
Hemp is a wonderfully sustainable, renewable resource and can be a fantastic material for mattresses. However, I’m yet to track down a crib mattress made with hemp. If one does exist, chances are that it’s a good option for a firm mattress in a hot and humid climate such as a nursery.
Hemp is one of the most breathable materials available. It can help a baby stay cool even in hot and humid temperatures and helps wick moisture away from their skin. This means it’s good for keeping the mattress feeling fresh, especially as hemp is naturally anti-microbial and anti-bacterial. Hemp is resistant to mold and mildew and doesn’t hold onto odors. That said, as with all crib mattresses, I’d be sure to cover any hemp mattress with a food-grade polyethylene waterproof cover and a puddle pad to help minimize the potential for soiling.
Some other things I like about hemp include its natural resistance to pests and its ability to grow so thick that it prevents weeds from growing nearby. This means that hemp cultivation typically doesn’t require the use of pesticides or herbicides, nor fertilizers as hemp actually enriches the quality of soil. And, because hemp roots grow deep, they are good at using groundwater and help reduce soil erosion.
The Pros and Cons of Coconut Coir Crib Mattresses
Most coconut coir crib mattresses are actually a mix of coconut coir and latex (sometimes natural, sometimes synthetic). Together, this mixture provides excellent firm support for a sleeping infant and it’s great that coconut coir is a renewable resource which is largely considered a by-product of the coconut water industry.
Consumer Reports have recommended coconut coir as an excellent material to make the insulating layer on top of innerspring coils. A thick insulator pad helps keep coils from poking through and a coir fiber pad appears to be much more durable than pads made with woven polyester. Polyester pads tend to form pockets and become concave in areas of the mattress frequently used. For a crib mattress, this could create a safety hazard for infants.
Unfortunately, while coconut coir mattresses sound like a great idea, a mattress filled with coconut coir will be a lot heavier than an innerspring mattress and may trap carbon dioxide as it is quite porous (as is latex). In theory, then, a coconut coir mattress might increase the risk of rebreathing carbon dioxide.
Indeed, a ‘breathable’ tea tree bark-filled mattress marketed in Australia in the 1980’s and ‘90’s did increased re-breathing of carbon dioxide and was associated with an increased risk of SIDS. Now, there’s no evidence that coconut coir mattresses would create such a problem, and there may well be other factors involved in the increased risk associated with tea tree bark (such as natural off-gassing), but I’d be wary of marketing hype trying to sell you a coconut coir mattress on the basis of breathability.
Also, while a coconut coir mattress may be marketed as being better for dissipating heat, there’s no evidence to support this either. As such, claims that this type of mattress reduces the risk of sudden infant death syndrome (SIDS) associated with overheating are also unsubstantiated.
There’s also the issue of coconut coir being blended with latex. Many companies don’t specify if that latex is synthetic or 100% natural. If the product doesn’t have GOLS certification or some other guarantee that it is made with 100% natural latex (usually Dunlop), be wary. Synthetic latex can contain some toxic chemicals and is not eco-friendly.
And, finally, it’s worth considering another potential health hazard with coconut coir: the effects of processing coconut coir on workers’ health. After many years of reports of adverse health effects on workers handling coconut coir, preliminary research has confirmed a higher incidence and apparent risk of respiratory and pulmonary symptoms in these workers (R). Given this potential, I’d be wary of buying a coconut coir product that isn’t certified Fair Trade or where working conditions haven’t otherwise been assessed for safety.
All in all, a mattress filled with coconut coir isn’t a terrible idea, but it is unlikely to be quite as magnificent as manufacturers would like us to believe and may pose a health risk for workers.
Pros and Cons of Innerspring Crib Mattresses
An innerspring mattress is an excellent choice for a crib mattress as it can be lightweight, comfortable, durable, and inexpensive. Innerspring or coil crib mattresses will often have a different level of firmness on each side, making them a great choice if you plan to also use a crib mattress for a toddler bed.
The comfort and quality of these mattresses largely depends on how many layers the mattress has and what goes into the layers, as well as the type of cover on the mattress. For instance, a high-quality mattress may have a central layer featuring steel coils wrapped individually in PLA (a corn-based bioplastic) and/or cotton, with a layer of latex or cotton batting, wrapped in a layer of wool, with another layer of cotton, and, finally, a waterproof cover made of polyethylene. Some innerspring mattresses have a layer of foam, though, so be wary and ask questions about the construction of each layer of a mattress before buying.
Innerspring crib mattresses that have dual firmness typically have a softer latex layer or foam layer for the ‘toddler’ side of the mattress and a wool or cotton batting layer for a firmer sleep surface for an infant. This isn’t strictly necessary, though, given that most toddlers will quite happily sleep on a firm mattress. Also, you can simply add a comfort layer on top of the mattress, such as a thin layer of Talalay latex after the age of one, should you wish.
While dual firmness isn’t essential, border rods are. In an innerspring crib mattress, border rods provide strong side and edge support so that the mattress doesn’t sag or compress unduly when a baby stands or walks on the mattress edge.
The number of steel coils or springs in a mattress can affect the quality of a mattress but they don’t always indicate how firm the mattress will be. Instead, a high-gauge is the best indicator of the spring unit in a mattress. For instance, one mattress may have 80 coils and another 250, but the 80 coils mattress may be firmer than the one with the higher spring count if the coils are made with thicker (higher gauge) steel. Gauge varies typically from 19 to 12.5, with the lower number indicating a thicker coil (oddly enough). For a crib mattress, industry experts generally suggest looking for a coil count of around 135-150 and a steel gauge of 15.5 or below.
The insulator pad is also important in an innerspring mattress as this helps stop the coils from poking through. As mentioned a moment ago, coir fiber is a good material for an insulator pad as it is strong, firm, and durable. Fiber wrap or rag or ‘shoddy’ pads are also used and are cheaper and, some argue, just as effective. Woven polyester pads are liable to form pockets over time and should be avoided as these may create a safety issue for infants. Hard, pressed felt is also used as an insulator and can be an excellent material choice.
On top of the insulating pad is the cushioning layer or layers. This is usually made with foam, cotton, or polyester, but may be made with wool or latex. Polyester is cheapest but, again, tends to form pockets which make the mattress less durable and potentially unsafe for an infant. An innerspring mattress with a layer of Dunlop latex, topped with wool and a layer of cotton, plus a waterproof cover made with polyethylene would be my choice for a lightweight, eco-friendly, non-toxic crib mattress.
A word about polyurethane, TPU, and polyethylene
Polyurethane foam is one of the most common materials used to make crib mattresses. It is a versatile material made with petroleum and blowing agents. It is also highly flammable and could potentially expose your baby to dangerous chemicals that can cause respiratory irritation and skin irritation, and adversely affect the immune system, endocrine system, reproductive health, and cognitive development. I’ve written more about polyurethane in the What To Watch Out For article in this Leaf Score series on crib mattresses.
Clearly, then, I don’t recommend buying a mattress made with polyurethane foam, but if you are considering a foam mattress there are ways to make a safer choice.
First, check where a company sources their foam. If it is made in the U.S. or EU it is subject to stricter safety regulations than foam made in many other regions and countries. Second, look at how dense the foam is. Foam can range from around 2.5 lbs to more than 5.5 lbs per cubic foot. Foam under around 3 lbs is considered low density and typically feels soft. This kind of foam is usually too soft for a crib mattress, but you don’t want to go too dense as higher-density foams contain more polymers and, thus, require more resources to make and have more chemicals to off-gas.
There are also various certifications that offer some assurance that the toxic chemical content of a foam mattress may be lower than for similar products. So, if you’re buying a foam crib mattress, look for a Greenguard Gold and/or Oeko-Tex Standard 100 or 1000 certification. These certifications by no means guarantee that a product is non-toxic or eco-friendly, but they do suggest that a product might be a tad less problematic than its uncertified counterparts.
Finally, you’ll want to check how the mattress meets safety requirements for flammability. If a product is coated in chemical fire retardants, avoid it and look for one that has an outer cover made with something like Rayon, silica and Kevlar (check that this doesn’t just apply to mattress seams). These materials are far from eco-friendly, but they can help reduce the amount of chemicals that need to be applied for a mattress to meet fire safety standards.
Plastic waterproofing for crib mattresses
Given how babies are, shall we say, generous with fluids, I highly recommend waterproofing your crib mattress. However, I don’t necessarily recommend mattresses that feature a waterproof cover made with TPU (thermoplastic polyurethane), which is another petroleum based synthetic polymer.
TPU is similar to polyurethane, but is more water resistant, does not contain crosslinks, and has hard and soft segments that make it more durable, elastic, and resistant to stretching and stains than polyurethane. Compared to PVC and polyurethane, TPU is less likely to degrade and crack, meaning that the waterproof covering of a crib mattress will stay waterproof for longer.
TPU is made from polyether, polyester, or polycaprolactones, while polyurethane is made from polyols and isocyanates. In general, TPU could be considered less toxic than polyurethane, given that it doesn’t contain problematic isocyanates and polyols. TPU is, in fact, used in biomedical applications and is considered an inert material, depending on exactly how it was created.
If there are monomers and catalysts left over from the polymerization reaction(s) and other processes used to create TPU, there’s a chance that these could pose a risk of toxicity. Also, other chemicals may be added to TPU which could compromise its safety, and the degradation of TPU may produce unsafe degradation products, including toxic gases and dust. As with polyurethane, burning TPU produces irritant toxic fumes, meaning that any mattress made with TPU will probably have been treated with flame retardants.
Plastic is currently the only viable way to completely waterproof a mattress, but it’s worth noting that different types of plastic have different levels of toxicity for human health and the environment. If you’re faced with a choice between polyurethane, PVC, and TPU, TPU is probably your best option for a waterproof mattress cover. Your best bet, though, is to go for a mattress with a food-grade polyethylene cover. Some companies, such as Naturepedic, use polyurethane to waterproof their GOTS-certified mattress pads but use polyethylene for the waterproof covers on their waterproof mattresses.
Polyethylene is considered safe for wrapping food and is arguably your best bet for a truly waterproof material to protect both a crib mattress and the infant sleeping on that mattress. This type of polymer is both the simplest of all commercial polymers and the most popular type of plastic in the world.
Polyethylene is the plastic used to make grocery bags, toiletry bottles, sandwich wrap, and even bullet proof vests. The strength of the plastic depends on its molecular structure, which basically consists of a long chain of carbon atoms with two hydrogen atoms attached to each carbon atoms. Once this chain begins to branch off into other chains, the plastic becomes softer.
While it’s often touted as being non-toxic and entirely safe, polyethylene is still a synthetic material produced using potentially problematic chemicals. The chemical reaction required to create polyethylene seems to involve a transition metal catalyst, like TiCl3, or titanium trichloride, and co-catalysts such as group III metals like aluminum. The type of low density polyethylene used for waterproof mattress covers does not, however, typically contain bisphenol-A (BPA), a known endocrine disruptor.
Like all plastics, polyethylene will eventually degrade with exposure to sunlight, heat, and moisture, and it may release toxic gases when this happens. Polyethylene also breaks down very quickly if washed with warm water, so you should never machine wash a polyethylene cover or mattress.
Given the high risks of mold, mildew, bacterial, and fungal infection in a crib mattress, however, I’d lean towards choosing a mattress with a polyethylene cover and simply cover this with a puddle pad and organic cotton sheet for added protection and some protection against potential off-gassing. I’d also air out the mattress for at least a few days before placing an infant on the mattress to sleep.
Oh, and beware of mattresses marketed as being made with ‘eco-foam’ or soy-based foam. These so-called green mattresses or plant-based mattresses are still made with petroleum-based polyurethane foam, it’s just that the company throws in a little soy oil (usually less than 20%) so they can call it eco-friendly. These foam mattresses are still highly flammable and riddled with toxic chemicals, including the flame retardants usually required for them to meet federal fire safety standards.
Alternative mattress cover materials
For decades, most mattress covers have been made with PVC. This plastic material is cheap, easily cleaned, and quite effective as a waterproof surface. However, PVC is not at all environmentally friendly and is made with toxic chemicals that may leach or off-gas as the PVC degrades, which it will. As such, ‘green’ mattresses often don’t feature a vinyl cover and instead have cloth covers made with cotton or bamboo. Unfortunately, in addition to not actually being waterproof, these covers are also not necessarily eco-friendly or non-toxic.
Bamboo, as I’ve talked about before at Leaf Score, is an incredible renewable material and can be non-toxic and eco-friendly when used in certain ways. As a fiber for textiles, bamboo is generally not eco-friendly or non-toxic, however, and is typically processed with harsh chemicals in an energy intensive way to break down those tough natural fibers. Bamboo rayon, rayon, or Tencel are not eco-friendly materials and are instead synthetic fibers made from bamboo. So, don’t be fooled by greenwashing.
As for cotton, this is a great material for a mattress cover, assuming it is organic and hasn’t been subjected to chlorine bleach or toxic dyes, or antimicrobial treatments and other chemical processes. Cotton isn’t waterproof, however, so it should be used on top of a waterproof layer of polyethylene and, ideally, wool. If you absolutely want to avoid plastics, a combination of organic cotton on top of wool on top of cotton on top of wool may be the way to go. The cotton will absorb leaks and the wool wicks moisture away, which can help keep a mattress dry.
The thing to remember is that organic fillings are subject to organic processes, and these organic processes are not always harmless. Wool, coconut coir, cotton, and other natural fibers can create a lovely home for microbes and bugs, as can polyurethane foam and other synthetic materials. Your best bet, then, is to make sure your baby’s crib mattress is well protected against moisture and undesirable critters and single-celled organisms with an effective waterproofing strategy such as polyethylene, which will also keep out bugs.