Durable polyurethane keel rollers, from the Stolz brand, surpass their rubber or PVC counterparts in terms of strength and longevity. Although they are a bit more expensive, you will probably never need to replace them. Moreover, their surface leaves no streaks on the boat hull, keeping it looking neat at all times. Also, PU rollers stay round and show no flat spots if the boat has been standing on them for a long time!
Metal core
Polyurethane rollers have a hard surface and metal core, making launching your boat easier.