Here is what someone e-mailed about this question of yours. Please read below......
Personally I have been the proud owner of the Tempur-Pedic Classic Sleep System for a little over three years now. My mattress is still in mint condition and I weigh 170 lbs. and my husband weighs 240 lbs. I do not have a permanent indention that I roll into every night.
Tempur-Pedic mattresses are temperature sensitive and breathable. While some people do say they find the mattresses hot, many of them were hot on inner spring mattresses. The mattress itself will increase your circulation due the increased support it gives your body. Although our cover is breathable, it does create a light barrier that inhibits the complete absorption of body temperature into the TEMPUR® material.
The warranty covers up to ¾ of an inch in sagging if it occurs in the first 10 years. After 10 years the warranty is pro-rated. You can view the warranty @ www.tempurpedic.com