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Better known as TPX® from Mitsui Chemicals. Inc.. Polymethylpentene is a thermoplastic polymer. It is a lightweight. high temperature polyolefin with exceptional acoustical and electrical properties.

TPX® Polymethylpentene (PMP) characteristics are similar to those of traditional polyolefins and include excellent electrical insulating properties and strong hydrolysis resistance. In addition, TPX® features low dielectric, superb clarity, transparency, gas permeability, heat resistance, and release qualities. Chemical resistance and electrical properties of TPX are similar to those of other polyolefins except it retains these properties at higher temperatures than PP or PE.

This Polymethylpentene can be used for extruded and film products, injection molded, and blow molded application items. Because of its high melting point and good temperature stability, polymethylpentene is used for autoclavable medical and laboratory equipment, microwave components, and cookware. It is also often used in electrical components such as LED molds because it is an excellent electrical insulator.

Brand Names

  • TPX®
  • Unitene®
  • Westlake Pmp

Emco Industrial Plastics doesn’t claim to represent all of the manufacturers or trade name products listed. This list is intended as a guide of typical materials available for purchase from Emco Industrial Plastics, Inc. For additional information, contact an Emco Industrial Plastics representative by filling out the form below.

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At a Glance

Generic Name
Polymethylpentene, Copolyme

Available In
Sheet, Rod, Tube, Film

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Technical Information

Stock Products Properties Applications Advantages

Stock Products

Sheet 1/4″ – 4″ TH Natural
Rod 3/8″ – 4″ DIA Natural
Tube CUSTOM Natural
Film 0.002 – 0.029″ TH Natural

Give us your cut-to-size dimensions. We will precision-cut these plastics to your exact size. Additional sizes and colors available upon request.


Physical PropertiesUnitsASTMResults
Density lb/in³ D792 0.045
Water Absorption, 24 hrs % D570 0.3
Mechanical PropertiesUnitsASTMResults
Tensile Strength @yield psi D638 10200
Tensile Modulus psi D638 360000
Tensile Elongation @Break % D638 30
Flexural Strength psi D790 15000
Flexural Modulus psi D790 400000
Compressive Strength psi D695 13000
Compressive Modulus psi D695 375000
Hardness, Rockwell R D785 M82/R128
IZOD Impact Strength Notched ft-lb/in D256 1.3
IZOD Impact Strength Un-notched ft-lb/in D256 NO BREAK
Thermal PropertiesUnitsASTMResults
Coefficient of Linear Thermal Expansion (x 10⁻⁵ in./in./°F) D256 3.1
Heat Deflection Temp at 66 psi °F D648 358
Heat Deflection Temp at 264 psi °F 340
Melting Temperature °F D3418 374
Max Operating Temp °F 300
Thermal Conductivity BTU-in/ft²-hr-°F C177 3.1 x 10⁻⁵
Flammability Rating UL94 HB
Electrical PropertiesUnitsASTMResults
Dielectric Strength V/mil D149 425
Dielectric Constant 1MHz D150 3.14
Dissipation Factor @ 60 Hz 1MHz D150 0.0008
Volume Resistivity, 50% RH ohm-cm D257 5 x 105 x 10¹⁶

NOTE: The property values presented above are typical values intended for reference and comparison purposes only. They should NOT be used as a basis for design specifications or quality control. Contact us for manufacturers’ complete material property datasheets. All values at 73°F (23°C) unless otherwise noted.


  • Medical instrument covers
  • Electrical parts
  • Sound Equipment-speaker cones
  • Release Film
  • Wire and Cable Applications
  • Membranes
  • FDA compliant grades for use in food processing machinery


  • Optically clear
  • Good Chemical Resistance
  • Low specific gravity
  • Good Electrical Properties
  • Good Heat Resistance
  • Low Moisture Absorption
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