Synastren posted:

I sure hope someone doesn't ask an industry specific question that can have a needlessly convoluted answer that I did entirely through my own research over the last few years.

<clicks thread>

Oh gently caress me

short version: Phase change material is a catchall that generally means "wax that melts at skin temperature." PCM cools more intensely than virtually any other technology but typically only for a maximum "cool" of 30 minutes. From there, it continues to work but should be considered something that fights against overheating. Likely the closest thing to real life, actual "cooling gel."

Longer, more in-depth explanation that you probably won't even get if you work in the industry and I have pieced together myself because of my insatiable curiosity:

Phase change material refers to a substance that changes its physical state (liquid, solid, gas), typically at useful thermal levels. The one we're most used to is water, particularly its relationship to ice. Ice maintains its temperature, regardless of its surrounding environment, but it absorbs relatively huge amounts of heat when it melts. It is this change in physical state, aka phase change, that is significant, as it is what we rely on to cool things with ice, since it absorbs so much heat! This is also why water is so useful for a number of cooking techniques, as boiling water cannot typically go beyond its boiling point--it evaporates instead, thereby changing its physical state. Think of water as something that has a consistent temperature band, and that requires relatively massive amounts of thermal energy to cross a breakpoint to get to a different physical state.

PCM in bedding is typically paraffin wax in a gel suspension, typically in little balls. From there, things can vary wildly from treatment to treatment, from vendor to vendor. In pillows, for example, it just looks like a product has been sprayed with a blue gel because the globules are very small. In contrast, in Tempur's breeze line of mattresses, the globules are actually significantly larger than everyone else's variation. To continue the ice analogy, the larger the chunk of ice, the longer it takes to melt, the longer it takes to lose its cooling properties; conversely, if the ice bits are smaller, the cool will be much more intense for a lesser amount of time. This analogy maps on well to PCM globule size. You can also see it yourself with the difference in performance and duration of something like a whisky sphere vs a standard ice cube vs crushed ice. Similarly, PCM treated pillows will typically be intensively cool, but that cooling will last no more than 20 minutes--some as short as 5 or 10. Most mattresses that use PCM should stay cool (read: not cold, but cool) for about 20-30 minutes. Tempur's breeze PCM outperforms that but I don't know the exact numbers, and there are so many things in that mattress that it would be impossible to test without destroying the mattress or Tempur telling us.

It is also worth mentioning as clearly as possible that PCM only feels cold until it melts. Once the treatment directly under your body is melted, it will continue to push heat to the parts not directly under you, but it will no longer feel cold. You know, like ice does. Unlike ice, though, because its melting point is also its freezing point when you remove a heat source, it can rapidly resolidify once that heat (i.e., your head) is moved to another part of this hypothetical pillow.

Unlike ice, PCM can have different melting point temperatures which can also affect its cooling. The most common melting point for the aforementioned wax is typically somewhere between 84 - 86 degrees F, as that is the average skin temperature. In sophisticated cooling treatments (the now dead BeautyRest Black Ice foam mattresses, for example), they had three different layers of PCM each with a different melting point that ascended, which provided a much prolonged cooling performance that was also intensely cool. And it also cost about $5k for one of those about 4 years ago, so you certainly paid for it. The best performing PCM, if globule size is held constant, will have multiple melting points, which you can think of analogous to an onion. When one layer is used up, there is another underneath.

The final thing to mention is that some companies are toying with other ways to generate PCM. BeautyRest has started using PCM derived from sunflower oil, which is pretty cool.

So, in summary, the cheapest PCM treatment will be a thin layer of something that feels pretty cool for about as long as you want to stand at an in-store demo at Bed Bath and Beyond in order to get you to buy it. The more common treatment in a relatively upscale pillow will look similar, but will be fairly intensely cold for about 5-15 minutes before the PCM is exhausted. In a mattress, double that estimated time. At the upper end, you can probably expect to be that cold from the PCM for maybe half an hour.

Note, however, that for best results, PCM is utilized in tandem with other cooling technologies, particularly fabrics that feel cold as well, or components which are extremely breathable. You do not want to rely on PCM as the only cooling technology in a product if you are looking for something more than a cool surface to help you fall asleep!