I have been around race cars my whole life. Every car needs roll bar padding. Now days they make fire retardant padding for that purpose. But years ago, the most common thing to use was foam pipe insulation that you can get at any hardware store. It comes in many sizes, so if your bar is say 1" buy 1" padding. Then when you have the padding on the bar, wrap it tightly with black tape. The tape keeps it on the bar and by wrapping it tight it compresses it so it don't move. Wrap the entire piece of foam, not just several spots. It gives the foam protection from rubbing, ripping, absorbing water etc. It might sound crude but it works very well.