Hi cedarhunter,
In addition to the information in this post … post #29 here has more information about temperature regulation and the microclimate on a mattress.
There are many factors which control the sleeping temperature of a mattress and only one of these is the foam that is used in the mattress … particularly in the upper layers.
There are 3 main types of foam which is memory foam, polyfoam, and latex. Of these three … memory foam tends to be the most insulating and least breathable followed by polyfoam and latex is the most breathable. Talalay tends to be more breathable than Dunlop. There are also variations in each category and less dense foams tend to be more breathable than denser foams while firmer foams tend to allow less sinking in which can mean there is less insulating foam material against your body.
All foams are insulators (rather than heat conductors) so to some degree they will all be warmer than mattresses that contain no foam at all (such as mattresses that only have an innerspring and layers of natural fibers on top) but these tend to be premium or super premium mattresses and for the most part almost all mattresses have some type of foam in the comfort layers.
Some of the other factors involved in how warm a mattress sleeps are how closely the foam conforms to your body (the more closely it conforms around you the more insulating it is), how soft or thick the foam in the comfort layers are (the softer/thicker it is the deeper you will sink into the more insulating materials), the type of quilting used in the mattress (natural fibers allow for more airflow and humidity control which translates into better temperature regulation), the type of ticking (cover) used (natural or more breathable fibers such as cotton or viscose or even some of the more breathable synthetics will wick away moisture and ventilate better and humidity control is a key part of temperature control), and on any cooling technologies used in the mattress such as ventilating and moisture wicking materials, heat conductive materials, or phase change materials (you can read more about these in post #9 here and at the end of post #4 here) and you can read more about the various different types of gel foams in post #2 here. In general terms gel foams will tend to have a temporary effect on temperature while you are first going to sleep until temperatures equalize but have less effect on temperature regulation throughout the course of the night.
While the upper layers of a mattress are the most significant part of temperature and moisture regulation … deeper support components that allow more airflow can also have an effect and so innersprings will also tend to sleep cooler than foam support cores as long as the air can ventilate to the outside of the mattress.
In addition to this … the mattress protector you choose along with your sheets and other bedding and what you wear when you sleep will also have a significant effect on temperature regulation because they can either add to the insulating effect or to the ventilating and moisture wicking effect of your mattress. You can see more about the effect of different mattress protectors in post #89 here. Bedding made from natural fibers or viscose materials (like bamboo) will also tend to be cooler than synthetic fibers and linen sheets along with silk are probably the coolest of all the natural fibers for those where sleeping temperature is a main priority. There is more about sheets and bedding in post #7 here. In many cases changing the mattress protector, sheets, or bedding to cooler versions can make “enough” of a difference for many people who would otherwise sleep hot on a mattress.
All of this of course is separate from any environmental conditions in the bedroom (temperature and humidity levels with higher humidity adding to the perception of heat), on the physiology and tendency of the person themselves to sleep warmer or cooler and where they are in the “oven to iceberg” range, and on their weight and body type which will affect how deeply they sink into the foam layers of the mattress.
In other words … it’s always a combination of several interacting factors that determines the sleeping temperature of a mattress in combination with a specific person and environment.
Overall … if you are looking at a mattress that contains foam of some type … then latex with natural fibers in the quilting (such as wool) and fabrics that can wick away moisture and help it evaporate more rapidly are the coolest sleeping or more accurately the most temperature regulating mattresses and firmer will tend to be cooler than softer.
Mattresses that don’t use any foam at all and only use an innerspring with natural fiber comfort layers will tend to be cooler and more temperature regulating than any type of foam including latex.
All types of latex come in firmer and softer versions which along with the layering (especially the thickness of the comfort layers) will determine how supportive the mattress is and how well it keeps you in alignment in all your sleeping positions. Different types of layering can be more or less suitable for different weights and sleeping positions to balance the competing needs of pressure relief and support/alignment. While Dunlop has a higher compression modulus and will be firmer than Talalay in the same ILD (which is why Dunlop is often used in support layers and Talalay in comfort layers) … both of them can make good choices both in terms of pressure relief and support in appropriate layerings and the choice between them is generally one of preference (they feel and respond differently). This article and post #6 here has more about the different types and blends of latex.
Hope this helps.
Phoenix