The open secret is the open cell polyurethane foam. This is the only material that can do the two things of completely holding the foot back from sliding forward in heels - it is strong enough to not collapse PLUS it is soft & springy underfoot & never crushes so the ball of the foot is made as comfortable as can be. You can walk/stand/dance for about four times longer than you could with nothing in your shoes. PORON foam is much more shock absorbing than vinyl or gel inserts, plus it never gets slippery & is not bulky so it does not force your foot out of your shoe & cause instability under the heel of your foot. Inserts in high heels should never increase the height of the heel by placing a layer of material under the heel.This is counterproductive since high heel inserts should always be trying to make heels more comfortable to wear not less so. Many 3/4 gel insoles or full length gel insoles go under the heel of the foot to help keep the slippery insole in place, not because it adds comfort. The ball of the foot is where the pressure is, not under the elevated heel.
*PORON open cell polyurethane foam provides maximum repeated shock absorption from minimum thickness (The sculpted inserts toe grip & arch pad pieces are 6mm (1/4"), & taper to 1.5mm (1/32") at the edges. *PORON Performance Urethane has greater shock absorbency than gel. *PORON Performance material offers high-energy return & excellent shock absorption in high heels & flats. Feet in high heels are held from slipping forward so toes have wiggle room. *PORON is a trade mark of Rogers Corp.,CT, USA