The IsoCool mattress topper has a 3-inch, high-density visco-elastic foam mattress pad with a polyester cover. The IsoCool mattress topper features Outlast Adaptive Comfort material that adjusts to the body's changing temperature. The microscopic Phase Change Material (PCM) beads sense whether the body's mean temperature is too warm or too cool. If the body's temperature is too warm, the product absorbs heat and feels cool in order to regulate body temperature. If the body's temperature is too cool, the product releases heat and feels warm in order to regulate the body temperature. Carpenter Co.'s IsoCool products feature the highest available concentration of PCMs, making them extremely effective. IsoCool, Outlast and Adaptive Comfort are registered trademarks of Carpenter Co.