Wikipedia
Polymethylpentene
Polymethylpentene (PMP), also known as Poly(4-methyl-1-pentene), is a thermoplastic polymer of 4-methyl-1-pentene. It is used for gas permeable packaging, autoclavable medical and laboratory equipment, microwave components, and cookware. It is commonly called TPX, which is a trademark of Mitsui Chemicals.