Depending on the manufacturer, some carry a 1 year (I know, not much) warranty . Kimberly Clark makes some great materials like Evolution, Noah, etc, pricey, but nice. I bought mine through Wolf covers, and the seam at the spoiler cap began to seperate. Unfortunately, they were bought out by someone else and they will not honor the warranty... azz holes. I did talk them into some old material they had laying around, so I will stich in patches from the inside of the cover, at both spoiler cap corners, as well as the rear corners of the roof and hope for the best. Those 4 areas seem to take the most wear and tear.
But as covers go, you get what you pay for. I bought cheap covers for my Harley from Wall Mart, but they would only last 2-3 months at the most. I ended up buying a custom cover from Harley, it held up really well.