SiHy has a higher Dk than Hema. In the case of UltraHealth or Duette, the SiHy skirt has a Dk of 84 compared to previous hema designs which had a Dk of 9.

In the UltraHealth design the purpose of the SiHy skirt is to provide GP centration and edge lens comfort, not lift. This is important, because the SiHy skirt does not have the strength to permanently lift the GP off the cornea. While initially the SiHy may provide a temporary lift, after lens wear, the SiHy skirt does not hold up the lens and the lens settles down. That is why it is very important to fit the vault of the lens first, making sure that the vault clears the apex. Once this happens, then the skirt can be evaluated for optimum fit. Steeper skirts tend to be used in smaller, rounder eyes.