Polyurethane foam is an open cell foam with a soft sponge-like feel. Ideal for lightweight products. In its flexible form, polyurethane foam is common in packaging padding. In its rigid form, it's commonly used as insulation.
It's ideal for vibration dampening. When made into convoluted sheets, PU foam is commonly used as inserts for various equipment. Most commonly grey, but available in a variety of colors and densities.