Polyurethane (PU) foam is supplied almost exclusively with commercially sold cases, because it is the least expensive foam that the manufacturers can get. It is an open-cell foam, resulting in it being able to absorb liquids easily, which is not a desirable attribute. PU foam is available in different densities and hardness. For instance, 1570 PU foam has a density of 1.5 lbs. per cubic foot, and an IFD of 70. Indentation Force Deflection (IFD) is a scientific method of measuring relative foam hardness.