* 02: Aluminum* Precision-lathed 3.25'' aluminum roller drums run silent and smooth, and won't distort in heat or sunlight* Designed for both indoor and outdoor use* 03: Aluminum with resistance* The same great features as our aluminum rollers, with the benefit of additional resistance.* The unique patent-pending resistance unit uses zero moving parts to deliver 5 levels of quiet magnetic resistance.* Patents issued and pending* Fold flat or stand on end for convenient storage