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What Exactly are PCMs and How do They Keep the Mattress Cool?

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Online mattresses use various cooling techniques. Some use punctured foam while others combine foam with cooling gel. The Nest Love & Sleep mattress and several others use a phase change cover.

This is a type of cover embedded with PCMs or Phase Changing Materials.

A phase change cover is regarded as one of the best way to keep a mattress cool. But what exactly are these PCMs and how do they work?


Phase change materials have been used for years in many insulation applications where a constant temperature range is extremely crucial.

Here's how they work.

When temperature rises, they warm up and melt. They absorb heat during this phase change, causing the surroundings to cool. The opposite happens when temperature falls. They freeze and release heat, warming up the environment.

This principle works really well in phase change mattress covers. The cover keeps you in a sweet spot that is ideal for sleep – not too cold and not too warm.

If temperature approaches either extreme, the PCMs react to bring things back to the perfect range.

Here’s a more detailed explanation of how PCMs work in mattresses.

PCMs in Mattresses

Zotto Sleep
The Zotto mattress contains PCMs in the memory foam

When you get into bed, you start warming up gradually as heat released by your body is trapped underneath the bedding and in the mattress foam.

This is all good until the bed gets too warm from the trapped heat. Memory foam mattresses are especially notorious for getting overly hot because they retain more heat.

That’s when the PCMs kick into action.

Depending on the type of PCMs used, they will react when the temperature rises to a specific point.

Before that they will get warm alongside the mattress. But once the trigger temperature is reached, the PCMs begin to melt into a liquid.

This is where it gets interesting.

As the phase change materials melt, they absorb a lot of heat from the surrounding, in this case the bed. But the PCMs themselves do not get warmer. It's like blowing a balloon without inflating it.

PCMs can store huge amounts of heat without a change in temperature.

As they absorb heat, the mattress quickly cools down.

It also works the other way when the bed gets too cold.

The PCMs also get cooler until the trigger temperature is reached. They then freeze back into a solid. As they freeze, they release the stored heat into the environment.

Again, they do not change temperature even as they lose heat.

This warms up the bed again.

As the PCMs oscillate between these two phase changes (solid and liquid), they keep the mattress within a comfortable temperature range, never letting you get too warm or too cold.

Here's a visualization of how PCMs work.

How PCMs work
Credit: Microtek Labs

PCMs in mattresses are usually added to the cover, rather than the foam underneath, because they work better when they are very close to your body.

But a few mattresses, like Zotto, add PCMs to the foam layers, usually the top layer.

Types of PCMs

Different PCMs have different temperature ranges. Manufacturers choose those that will maintain the mattress at the ideal sleep temperature range.

Companies don’t usually announce which PCMs they have used. But most use special waxes (Polyolefins) in form of polymer chain links or encapsulated gels. They’ll often use more than one type of PCM in the mattress to achieve better temperature control.

Who Should Buy a PCM Mattress?

Anyone who needs a mattress that stays cool all the time.

If you are sensitive to heat as you sleep or you live in a hot climate, a PCM mattress will help you sleep more comfortably.

If you are planning to buy a memory foam mattress, it’s a good idea to find one that uses a PCM cover.

This is because memory foam traps a lot of heat and can make the bed too warm. A phase change cover will prevent overheating.

Mattresses with PCMs

Here are some of the mattresses that use phase change materials. It is not a complete list.

  • Nest Love & Sleep mattress – a 3 layer mattress consisting of Energex foam and poly foam. The PCMs are in the cover. See our review of the mattress here.
  • Cocoon mattress by Sealy – a budget memory foam layer with PCMs in the cover.
  • Zotto Sleep mattress – one of the few mattresses that incorporate PCMs in the foam rather than the cover.

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