Good afternoon,
One of my older fenders ( 26" x 10" - new cost $88+ USD ) has begun to leave marks on the
gelcoat. These marks that are difficult to remove. Otherwise, the fender holds air properly and prefer to extend it's life with a cover.
Have some scrap sumbrella and thought I make a fender cover since this
fabric is UV resistant and durable. I've just washed and dried a sample piece (12"x12") from the dryer to soften. As Sarafina mentioned,
washing helps. It's softened considerably with one wash.
Elf: the re-purposed "sweat pants" idea is brilliant.

The simplicity, expense (Goodwill for a practice pair) and the softer
fabric is appealing while replacing will be a breeze.
Fender covers help keep the
boat looking orderly since fender failure is random and identical
replacements aren't always available.
SM