I beleive the stock ones are a hard plastic, but on the case of the ones made by UPP, they use polyurethane which is "stronger, tougher, and more durable than products made with conventional elastomers and plastic. " ( there's a whole description of it here - http://www.uppracing.com/index.php?cid=109). I put Upp roller, chain slide, and rub block on my R 2 years ago and they show little wear and have held up great. but it's all up to you.