When comparing a memory foam vs. gel foam mattress, you should take note of any natural additives used. Some mattresses incorporate aloe vera or green tea extract, and others may include activated charcoal that absorbs volatile substances that cause odor. Some may even have an aromatherapy effect on you when you sleep, leaving you feeling much more refreshed when you waken up. They do not generally have any negative effect on you. They are added for their positive effects, and have never really caused problems unless you have an allergy to green tea extract or other chemical components of these additives. Such allergies are very rare. Such additives do not affect the cooling effect in any way.