Whether your workout takes you indoors or outside, stay comfortable in the Spenco PolySorb Cross Trainer insole. This removable insole features special heel strike cushioning to deliver optimum shock absorption for repetitive rear foot impact. The contoured layer of lightweight polyurethane in the Spenco PolySorb Cross Trainer insole is bonded to closed-cell nitrogen-injected Spenco Material for exceptional comfort and stability. Four-way stretch fabric reduces heat build-up that causes blisters and calluses.