The whole thing is rather suspect. The paperwork that comes with the topper deliberately avoids saying exactly how long the warranty is. You are told to register your product for the warranty on their website and when you do, it still does not tell you how long the warranty is. It does however offer an email address: email@example.com if you have questions.
I'm sorry, but I don't know about the warranty. We actually did not like it and returned it. We ordered a similar one that is a Serta, from Overstock.com and much prefer it. It is much more comfy than this one. It was a real HASSLE rolling it up and taping it up and shipping it back. But, that's what we did. And we were refunded.