Hi LookingNow,
Polyurethane is generally less dense (not more dense) than latex but it would also depend on the specifics of the polyfoam and the latex you are comparing because there is some overlap in in the range of latex and polyfoam densities.
Everlon is a 1.8 - 2 lb density polyfoam so it would have very different properties to memory foam (and it would be significantly less dense than 100% natural latex). It is normal for polyfoam to yellow or oxidize with exposure to the air.
There are several certifications that test for for harmful substances and VOC’s but they only identify whether a material is under the testing limits for that specific certification and don’t “rank” them relative to each other or specify which are “best or worst” on terms of safety. The most common certification for polyfoam and memory foam is CertiPUR and most of the US foam pourers are CertiPUR certified which for most people would be “safe enough” (although some people may still be sensitive to some materials that are CertiPUR-US certified that most people would be fine with). There is more about the different “safety” certifications in post #2 here.
ADMIN NOTE:Removed 404 page link | Archived Footprint: certipur.us/find-a-foam-supplier/
Phoenix