As builders learned to make more tightly-sealed houses in the 1970’s and 1980’s, indoor air quality deteriorated because the new, energy-saving designs limited the exchange of fresh air from the outside. One of the key issues builders of “green” houses face today is how to make the enclosure tight enough to minimize energy leakage, but also permeable to allow for healthful air circulation.
With mattress construction the issue is simpler because the only goal with mattresses is to increase air flow; there is never a reason to reduce it. You want a mattress to breathe. If heat or moisture builds up in it, a mattress becomes not only hot and uncomfortable, but also ripe for the growth of mold. Mold thrives in moist, dark environments.
The challenge for manufacturers is how to make a comfortable, durable mattress that breathes. Almost all mattresses contain foam of one kind or another as a cushioning material. Even innerspring mattresses include foam layers near the mattress top.
Three main types of foam are used in mattress production: memory foam, polyurethane foam, and natural latex foam (natural foam rubber). At the International Sleep Products Show in Charlotte, NC in 2010, Latex International did a nice presentation on the relative flow of air through each of these types of foam.
They forced air through solid pieces of memory foam, polyurethane foam, and latex foam–each in its own chamber. At the top of each chamber they placed an open-bottomed tube containing a ping-pong ball and allowed the ball to fly above the chamber.
Given the amount of same air pressure forced through each chamber and the same air flow through each piece of foam, you would expect the ping pong balls to rise to the same height. However, as you can see from the picture, the ball above the memory foam did not rise high at all. That’s because memory foam is so dense it tends to trap air, and along with it, heat and moisture. Many people who sleep close to memory foam describe how it feels a little clammy, like sleeping in damp sand.
Polyurethane foam performed a little better than memory foam because although the pressure was the same, the ping pong ball went higher. There is greater air flow through regular polyurethane foam than there is through memory foam. Normally people don’t sleep that close to polyurethane foam, but people typically report that it sleeps cooler and dryer than memory foam.
In this test natural latex proved to have the best air flow. In fact, the air pressure needed to be turned down on the chamber for the natural latex test, because the ping pong ball would have hit the top of the tube.
This simple demonstration confirmed the experience we hear about from so many people—a natural latex mattress sleeps “cooler” than those made with memory foam or polyurethane foam. Further, although customers usually don’t think of it, natural latex mattresses retain less moisture and humidity, so they’re less likely to develop mold or other bacteria or fungi.
For all these reasons, the air quality in and around a latex mattress will generally be superior to that near other foam mattresses, of course depending upon other materials used in the construction of the mattresses, bedding, and bed itself.