The final thing we considered while testing, although it’s not explicitly part of the above criteria beyond meeting certification standards, are the materials used in the mattress.
First, we looked at the core filling. Most crib mattresses either have a core made mostly of foam, or metal innersprings surrounded by cotton, polyester, or other materials. Some specialty crib mattresses are filled with food-grade polyethylene, natural cotton batting, or coconut husks. For every mattress we tested, we noted what was inside it.
Foam crib mattresses are generally lightweight, at about 5 to 13 pounds. Most foam mattresses are made of polyurethane, which is petroleum-based. Some types of polyurethane foam can contain formaldehyde (sometimes as part of an adhesive) and many mattresses advertise that they’re formaldehyde-free (CertiPUR-US certified foams are also made without formaldehyde, high levels of exposure to which have been linked to asthma). The foam in mattresses that are touted as “eco-friendly” or “green” are often made with a small amount of soy or plant-based oil, which is substituted for some of the petroleum-based oil that’s typically used in polyurethane foam (think under 20 percent, sometimes well under, according to the sources we talked to). Alternatively, some foam mattresses are made of bamboo fiber or latex foam.
Innerspring mattresses are typically a bit heavier, at 15 to 30 pounds. If you’re purchasing an innerspring mattress, you want to look at the number of coils and the thickness of the steel that’s used. The more coils and thicker the steel the coils are made of (represented by a lower gauge), the firmer the mattress. Because young kids don’t need that much support, 135 to 150 coils is plenty, experts say (crib mattresses range from 80 to 200-plus), and a 15.5-gauge or so coil (on a scale from 12.5 to 20) is plenty thick. Innerspring mattresses often have border rods that go around the perimeter of the top and bottom to provide extra firmness and sag-preventing side and edge support.
In addition to the springs and border wires, innerspring mattresses have cushioning layers often made of polyester, foam, or cotton, and an insulator pad made of coir fiber (shredded coconut shells) or woven polyester. The more layers and better-quality materials used in those layers and that insulator pad, the better the mattress.
Organic and specialty mattresses are typically made from organic cotton, untreated wool, natural latex (an alternative to petroleum-based foam), and coconut fiber. One specialty mattress we tested, the Newton Baby, is made of woven food-grade plastic—the same type used by the food-packaging industry in sandwich bags—and air; another certified-organic model is made of molded waves of polyethylene (Naturepedic’s patented “wavesupport technology”) covered in organic cotton batting.
Next, I looked at the mattresses ticking, or its outer layer. Some crib mattresses are covered with cotton brushed with food-grade plastic; others have a waterproof vinyl cover. Three-ply vinyl covers are thicker and less likely to rip, tear, or dry out with use than thinner vinyl covers. Some vinyl, like polyvinyl chloride, or PVC, contains phthalates—plasticizers that make the material softer and more pliable and that some studies have linked to hormonal disruptions in lab animals. There are strict regulations on some, but not all, types of phthalates, which is why some mattresses cover themselves by noting that they’re phthalate- or PVC-free.
I also looked at the mattresses’ construction. Some mattresses are seamless; others have a zipper or seams around the entire cover. Some mattresses with seams seemed much more durable or tightly sewn than others. The better the construction, whether that meant a seamless mattress or one with a snug zipper or tightly sewn seams—and you can tell the difference when they’re in front of you—the more likely the mattress is to last for at least three or four years.
The experts we talked with said that, unsurprisingly, the general rule is that the more expensive the mattress is, the better quality the materials. When we lined up our testers from lowest to highest priced, that certainly seemed to be the case. At the least expensive end, we had an innerspring mattress with no border wire around it and a single-layer vinyl cover, and another mattress with polyester fill and a single-layer vinyl covering. Most middle-of-the-road mattresses had either polyurethane foam (some with a little of that soy or plant-based oil mixed in) or more innersprings with a border wire, covered with a multilayer polyester cover. The more-expensive mattresses were often two-sided, with a firmer infant side and a more comfortable toddler side. Their covers were made of higher-quality materials, like organic cotton with waterproof backing; organic cotton brushed with food-grade polyethylene plastic; or a medical-grade, water- and odor-resistant knit fabric.
