Visible indentation or sagging of the mattress greater than 1 inch and not resulting from improper use, an improper bed, bed base or foundation. Please note a + or 15 mm variation in length, width and thickness is in the tolerance limit and can also be subjective to individual measurements taken from the center of the mattress. A manufacturing defect in the cover zipper. This does not include breakage of the zipper from improper or manhandling of the zipper. Any physical defects in the material or workmanship, subject to limitations described in this warranty.