Like arctic fleece? As long as they don't chew it it's ok. I've been using it for my foster bun Luna and she loves it. But I wouldn't trust my other rabbits with it as they love shredding fabric and might eat it. The good thing about fleece compared to other fabrics is that it doesn't unravel. So if you're going to use fabric bedding it is a really good choice.
You can try giving it to your buns, but watch them really closely. What helped for me, since it slides across the floor too easily, was to anchor the edges to the cage with binder clips. That way Luna could bounce around without sliding all over.