The insoles are made from a grippy material with small nubs that prevent sweaty feet from slipping. Scholl GelActiv - Open Shoes is suitable for sandals and open shoes with heels. The new Scholl GelActiv technology consists of a combination of two types of gel that have been proven to absorb even the smallest impacts and effectively reduce the pressure generated while walking and running. The firmer gel supports the arch and heel of the foot, while the softer gel provides optimal cushioning and shock absorption.