when looking for foam for an upholstery project, you have the choice of high density and medium density. so what's the difference? it's common to think that a foam's density would relate to how firm it feels but that's not actually the case. density correlates to the foam's durability. these high and medium density foams feel the same when you sit on them, but the high density foam will last longer. the blue foam is the high density and the white is the medium density. once the foam is exposed to air it will start to yellow, so don't be concerned when this happens. for foam that will get heavy daily use, like couch cushions or mattress toppers,
high density foam is the better choice because it will hold up over time the best. but for light or occasional use, medium density foam will be sufficient like for accent chairs and head boards. if you want to use foam outdoors, you'll want eva-dri and ez-dri outdoor foam. they're both medium density, but they're designed to let water flow through them rather than absorbing it like a sponge. the open cell construction also lets humidity and moisture evaporate quickly. ez-dri foam also has a built in fungicidal additive that inhibits fungus and mildew. this will help prevent stains and odor. for heavy indoor use, you'll want the high density foam.
for light indoor use the medium density foam will work just fine, and for outdoor and marine applications, use the eva-dri or ez-dri foam.