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Why Is It Damp Under My Memory Foam Mattress?

Nov 21, 2012

The Nest Bedding Blog shows up very well in most searches online, so subsequently we get email questions on a continual basis, like this one today:

"Dear Nest Bedding, my husband and I were making the bed this morning and felt moisture under the memory foam mattress. We flipped it over and discovered that it is very damp under our mattress. What can this be from?"

Dampness, or moisture, underneath your mattress is a serious cause for alarm. It can lead to serious health issues, such as mold forming and proliferating inside of your mattress, and eventually releasing mold spores into the air. Mold spores can become an irritant and affect your breathing, they can even lodge in the mucous membrane of your lungs and cause serious issues. 

You are likely wondering how and why there is moisture under your mattress. The simple answer is that the moisture came from your body. Everyone sweats in their sleep, some, more than others. It can occur as simply as naturally sweating in your sleep to being a sign of a serious health issue, but everyone emits some sweat in their sleep. I have read how some people can sweat up to a pint or more during the course of an evening. If you sweat profusely you may want to consult a physician.

But moisture under the bed, the accumulation of your sweat, is a serious but easily remedied issue. You mentioned you had a memory foam mattress, and part of the issue is because you have a memory foam mattress. Some models and brands of memory foam mattresses and bed will sleep hotter than others, due to factor of construction and materials used. For example, most memory foam mattress brands are covered with plastic. That is, polyester fabrics. These fabrics have fancy names such as microfiber, and other trade names, but they are made with plastic nonetheless. One of the more popular Chinese made brands of memory foam mattresses claims to have a hemp and cotton blend, but it is actually 60% polyester. The problem with plastic fabrics is they are unable to absorb moisture and can lead to a hotter sleep surface.

Another issue with memory foam beds is they are usually 100% synthetic, and very dense, which also leads to a lack of airflow and heat retention. I know that one leading brand even mandates you put their foam bed on their box spring or it voids the warranty, yet the box spring is a solid piece of fiber board, further cutting off potential air flow. 

And yet another potential for making you sweat can be polyester and polyester blended sheets, comforters, and even down and feather comforters. These materials trap heat and restricts air flow, and also do a poor job of absorbing your body's moisture. It's the absorption that allows moisture to pulls away and evaporate. Plastic does not absorb it, allows it to pour through the bed and get to the bottom of the mattress.

Once the moisture gets to the bottom of the memory foam mattress, as you are experiencing, it has to go somewhere. If you have a breathable, supportive base, it simply evaporates. However, if your mattress is on the floor, on a solid, non-breathable base, or the slats are too plentiful or too wide, or simply too close together, the mattress cannot breathe properly and you accumulate moisture and eventually mold. I have even seen one situation where the mattress was on proper slats, but the customer had so much junk stuffed under their mattress that is cut off the air flow and led to mold.

So, in review: whether you have a memory foam mattress or organic latex mattress, it must be on a slatted, breathable base, or breathable box spring, or it will accumulate moisture and eventually mold. If you are sleeping hot, consider replacing your bedding with natural, synthetic-free bedding. If you use down and feather comforters, consider switching to wool as it's better at temperature regulation. If you are sleeping hot and have a memory foam mattress, consider adding a wool topper or switching to an all-natural organic mattress comprised of natural cottons and wools, which breathe much better.




  • Moisture Beneath Mattress