Hi mister,
As you can see from the posts I linked in my last reply the issue of the sleeping microclimate on a mattress is a complex one and each layer of a mattress … especially the ones that are closest to the body … contributes to the overall effect in one way or another and of course there are many other factors involved such as how deeply you sink into insulating materials that have different ventilation levels (this is connected to the comfort of the mattress). Hopefully this will fill in any gaps that aren’t in the other posts I linked.
Many years ago … I was a long distance bicycle tourist and the temperature issues that had to be dealt with were similar in the sense that a layered approach to ventilation and humidity control was always more effective and different layers where used to deal with different conditions. A lot of bicycling clothing is made of wool because of its ability to store moisture and perspiration without feeling wet (it stores moisture inside the fiber itself) and regulate temperature but underneath this we would often use cotton because of its ability to wick moisture away from the body into the wool. Cotton doesn’t however store moisture as well as wool without feeling wet. The circumstances were slightly different because of the greater extremes of conditions that are faced in cycling rather than the more constant conditions that are dealt with on a mattress but with a mattress the layers can’t be changed as easily either so they need to work for all the possible conditions that are experienced on the mattress. In both cases … the principle of layering is the same. It’s also interesting to note that perspiration itself is a form of phase change cooling as moisture changes from a liquid into a vapor and absorbs temperature and takes some of the heat away as it disperses.
So each layer in a mattress can either add to or detract from the other layers that are involved in the microclimate and their ability to ventilate (add to the dispersal of heat and water vapor) as well as wick moisture and store moisture away from the body is all part of the puzzle.
The foams in the comfort layers are a part of this. All foams are insulating materials but some are more breathable (which can allow for the dispersal of heat) than others. In addition to this … if you add gel or other thermally conductive materials or phase change materials into the foam this can have an effect as well (on temperature until it evens out but not on ventilation which is more important in the longer term). Next above the foam is often the quilting layer which can be either more foam or natural or synthetic fibers. Next above this is the fabric used in the mattress ticking itself. Next is the mattress protector, next is the sheets, and then comes the person (and what they are wearing) along with the layers on the other side of them which is their blankets and bedding. All of these play a role. If any of these layers “stop” the ventilation then you have dead air (insulating) and temperatures can go up. If moisture isn’t wicked away from the body … then you lose some ability to disperse heat.
A mattress protector is a good example and you can see the different types in post #89 here and the pros and cons of each. If you use one of the types that have a thin membrane which is waterproof but allows water vapor to go through … it will be less breathable and can add to the sleeping temperature of the mattress because it can’t disperse the water vapor as easily as a wool or stretch knit cotton protector and can “negate” some of the effect of the layers below it and add to the insulation effect instead of the ventilation effect. People choose these because they are thin and can have less effect on the feel of the mattress and can have a high level of protection against liquid spills but the tradeoff is that they can raise the temperature. Those who want water resistance (not waterproof) but a more breathable mattress protector that is much more temperature controlling and effective for all but the worst spills would choose wool and then others who want something more breathable yet that has little effect on the feel of the mattress but that only absorbs moisture (from normal sleeping) but may not provide great protection against accidents (unless you remove them quickly) and doesn’t “resist” liquids would choose cotton.
The goal of a mattress protector is of course to prevent stains which void the warranty (it’s not the protector itself but the stains that affect warranty coverage). No manufacturer I know of mandates a specific mattress protector and this is just a sales technique to get you to buy an extra product. In some cases the protectors themselves have a “so called” guarantee connected to them about staining the mattress that kicks in if you buy them together but these may not be as effective as choosing wisely in the first place (they will often just send you a stain removal kit instead of replacing the mattress for example or will find other reasons to avoid a mattress replacement in case of a stain).
In general a simple guideline to use is that in terms of foam in the upper layers … latex is the coolest, followed by polyfoam, followed by memory foam. Softer foams are more breathable which is one reason why a thin layer of soft and breathable quilting foam is used but they also allow you to sink in more which increases the body surface area that has an insulating layer against it.
In terms of fiber (used in either the quilting layer or as a fabric in the ticking or mattress protector) natural fibers are the most effective in terms of wicking and or storing moisture because synthetic fibers generally absorb moisture into the spaces not the fiber itself. Artificial or “semi-synthetic” fibers (in between natural and synthetic) such as various types of cellulosic or rayon fibers (made from dissolved plant cellulose) are closer to natural fibers and do a good job of wicking moisture away from the body and ventilating…
There are also some types of synthetic fibers (such as coolmax) which are specifically designed to draw moisture away from the skin and disperse it to the rest of the layer which can be effective as well.
In terms of sheets and bedding … natural or artificial fibers (cotton or various cellulosic fibers) are more cooling than synthetic fibers and linen is perhaps the coolest of all.
The thermal conductive materials or phase change materials added to a layer can have a temporary cooling or regulating effect which can reduce perspiration in the short term but IMO they don’t replace the ongoing effect of ventilation and humidity humidity control so they are just a piece of the puzzle. Thermal conductive materials need to be close to the body to have an effect. Phase change materials can act more at a distance but should still be relatively close.
So this is a very “techie” subject and is the subject of ongoing debate and research but this at least covers some of the basics and can help people understand why all the components in the upper layers of a sleeping system closest to the body can have a cumulative effect and why in some cases just the choice of the “wrong” mattress protector for someone that has a tendency to sleep hot anyway can put them over the line even if there are other cooling technologies in the mattress.
The “short” version is to choose more breathable foams, along with more natural fibers in all the mattress layers that you have control of.
In almost all cases … careful selection of the layers that you can control (such as a protector, sheets, and bedding) as well as environmental conditions (humidity and temperature), and avoiding various stimulants or other activities that can contribute to temperature issues before going to bed can help offset the ones you can’t control which may be contributing to the problem.
Phoenix