Hi Nari,
Sleeping is making some excellent points.
The sleeping temperature of a mattress is dependent on the sum total of a combination of factors and materials that can either wick moisture or water vapor away and store it away from the skin and/or allow for airflow to release it to the environment (see post #2 here and post #29 here). The moisture or water vapor is primarily what carries the heat away and keeps it away from the skin. No matter how breathable any material is … if you put a layer on top of it that doesn’t allow for airflow then the air underneath is trapped and becomes an insulator and traps moisture and heat against the skin. Just think for example of a leather seat or imagine putting plastic over a mattress which would generate heat no matter what was underneath it.
All foam including latex is an insulator but some are more insulating or breathable than others. Talalay latex for example as a category is the most breathable of the foam groups but if you put a fabric or other materials over it that doesn’t allow for airflow it can still sleep hot. If it is softer then you will sink into it more and it will “surround you” and be more insulating than if it was firmer and you sink into it less.
In addition to this … the Stearns & Foster latex mattresses use synthetic Dunlop latex which has lower airflow than other types of latex and in addition to this they use thick layers of polyfoam over the latex in the deeper layers which is at least 2" thick and usually more than this so you aren’t actually sleeping on the latex. This is also the weak link of these mattresses and the reason that so many of them develop impressions much more quickly than a “real” latex mattress (most of the current models use lower density polyfoam over the latex which is not particularly durable). Thick layers of polyfoam over latex (thicker than around an inch or so) is among the worst types of construction for a latex mattress because you lose many of the advantages of sleeping on a latex mattress.
This is also the reason that many manufacturers add either a thin layer of high airflow polyfoam quilting or synthetic fibers to the cover or better yet use a layer of wool quilting which can improve airflow over the latex and can also store the moisture inside the wool fiber away from the skin. wool can also be used as a fire barrier. Better manufacturers will also use covers such as cotton or another breathable fabric (such as linen or a rayon type fiber) that will wick the moisture away from the body and release it into the wool underneath it which can store up to 30% of its weight in moisture inside the fiber without feeling wet.
So your Stearns & Foster “so called” latex mattress is not typical of a “latex mattress” and you actually aren’t sleeping directly on latex at all but on polyfoam.
An innerspring is a deeper support component and while an innerspring is more breathable than any foam … it is also deeper in the mattress and the foam, fiber, and fabric layers over the innerspring (including your mattress protector, any mattress pad or topper you use, and your sheets and bedding) will have more to do with temperature regulation than the innerspring itself.
Phoenix