Hi MEKONG,
I apologize! I missed your reply, so please let me provide the information you were asking about.
You’re most certainly welcome.
I’m glad the information on this site has bene useful to you.
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.
The three main types of foam are 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 latex tends to be more breathable than Dunlop latex. 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. So that would be the general rule as far as a single piece of foam goes.
Regarding the memory foam, you may have come across various cooling memory foam claims, and you can read more about phase change materials 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.
With all of that being said, there are many other factors that will impact your overall sleeping temperature, including the type of mattress protector and the sheets and bedding that you use (which in many cases can have just as significant an effect on sleeping temperature as the type of foam in a mattress) and on where you are in the “oven to iceberg” range and because there is no standardized testing for temperature regulation with different combinations of materials … there is much more about the many variables that can affect the sleeping temperature of a mattress or sleeping system in post #2 here that can help you choose the types of materials and components that are most likely to keep you in a comfortable temperature range.
I know this information is a little late in arriving, but I hope it is still helpful to you.
Phoenix