PolySorb? Heavy Duty Replacement Insoles are proven to deliver the best combination of shock absorption and energy return. They help reduce friction while improving overall foot comfort. A contoured layer of lightweight polyurethane is bonded to nitrogen-injected closed-cell Spenco? material to provide oustanding cushioning and foot stability. These insoles return energy with special heel strike cushioning for people who are on their feet all day. Durable and washable.