 Some climbers believe polyurethane can become warm with intensive use, though a few moments of not being held and some brushing usually solves the problem.PU holds are generally a lot lighter than Polyester holds as PU tolerates a much thinner wall so it can be hollowed out and maintain strength whereas PE holds need to be solid or have very thick walls or they are much more prone to breaking.Polyurethane is the leading hold material in the USA.