This product is custom manufactured to the ISO specification. (Many items currently available are inferior/non-conforming off the shelf foams of Polyesterurethane type, which have different hardness and chemical properties.) To ensure improved shelf life and reduce yellowing through exposure to UV radiation in daylight, it is heat-sealed in a Black UV-stable Polythene pack. Available in packs of 25 sheets and 1,000 piece 38mm cut discs.