Polymethylpentene (PMP), also referred to as poly(4-methyl-1-pentene), may be 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 may be a trademark of Mitsui Chemicals. Polymethylpentene melts at ≈ 235 °C. It has a really rarity (0.84 g/cm3) and is transparent. It has low moisture absorption and exceptional acoustical and electrical properties. Its properties are reasonably similar to those of other polyolefins, although it is more brittle and more gas permeable. The polymer also has high thermal stability, excellent dielectric characteristics and high chemical resistance. The crystalline phase features a lower density than the amorphous phase. In comparison to other materials getting used for operating in THz range, TPX shows excellent optical properties with a wavelength-independent index of refraction of 1.460±0.005 between light and 100~GHz.