1/2" pipe insulation. 3/4" is too thick.

Also, it's the "foamy" kind like the pool noodles. There's a smooth black type that is too soft and tears too easily.

I secure each end to the bar with duct tape. In over 10 years, I have not had an issue with slippage of the foam, or my hands.m

I rotate between my bikes, but on the most ridden bike the foam usually lasts 6-9 months or so before squishing down. A six-foot length is good for three pairs of pads, and costs under 5 bucks, sometimes as little as $2.