Here’s an entire page from McMaster that has all the specs and info you could want for the traction material:
IFI Wheels come with both the Wedgetop or the rubber Roughtop. Some teams use the blue nitrile for wheel tread, but it’s noticeably more expensive, so it may not be worth it for you.
I believe the technical term is conveyor belting. Your choice of incline or food grade on McMaster. Choose your type (roughtop or wedgetop) and your material, but make sure it’s strong enough.