Hi eml,
This depends on the type of foam you mean. There are three broad categories of foam which are memory foam, polyurethane foam, and latex. Of the three, memory foam tends to be the warmest followed by polyurethane foam and latex is the most breathable of all of them
There there is a range of breathability and ventilation in all of these foam categories though (and all foam types will be warmer than a mattress that uses only natural fibers and no foam at all). Sleeping temperature also depends on many other factors besides just the foam used. Of the three though … memory foam is most closely connected with heat retention issues and they are less common with the other two. There’s more about the factors involved in temperature regulation in post #2 here and there’s more about the various methods used to “cool down” memory foam in post #6 here.
Latex … even in fairly “soft” versions can feel firmer than some people are used to at first … especially if they are used to sleeping on supersoft polyfoam or memory foam. Of course it could also be because of the firmness of the latex they use because I don’t know the ILD of the Simmons. Softness/firmness is very subjective and what some people would call soft others would call firm and this also depends on body type, sleeping position, and the sensitivities of different people. As I mentioned before though … it’s always easier to soften up a mattress that is too firm than the other way around. At least the materials are good quality.
Phoenix