The warranty is for one year. It is for manufacturers defects, though, not for usual wear with a cover lifter.
I did have a slight problem with my cover at the beginning of this year. I noticed that there was a tear in my cover, (this is kind of hard to explain). It was on the inside of the crease, just above the zipper that you use to open it up. It was vertical, and there was no obvious signs of abuse. It was the outer layer only, not the inner layer which keeps the foam from being water logged. (I'm not sure, but I believe it is closed foam on the inside, but the experts can tell you for sure).
I took pictures and called my dealer. (This is how I found out they no longer sell hot tubs.) They came out and took their own pictures. Hot Spring immediately replaced the skin, and I have had no problems since!!!
May I ask why you are asking?