Which of the two types have better compression set resistance - Open Cell Foams and Sponges, or Closed Cell Sponges?

The structure of closed cell sponge rubber has non-interconnecting, or individual cells that contain air - typically nitrogen gas. When force is applied to these cells, it causes the gas to be gradually squeezed through the thin cell membranes. Upon release of force, the cells attempt to return to the original shape, drawing air back into the individual cells. Some sponge materials rebound quickly and some rebound very slowly or take a permanent deformation. Materials such as closed cell silicone sponge are more resilient and are better suited to rebound to close to the original sponge thickness. Deflective force under high temperatures and severe deflection over 50% can potentially damage the cell structure and impact the ability of the closed cell sponge to resist taking a permanent compression set. Open cell foams and sponges have cells that interconnect, allowing for air to pass through them quickly under deflection - and air is drawn back into open cell material faster when the deflection force is removed. Open cell foams and sponges are known for fast rebound, and generally return to original thickness. Cellular (poly)urethane is an example of open cell foam with excellent compression set resistance.