CUSTOMER SERVICE : +33 4 74 76 12 66

Summer closure banner

What is O-PET (OKP-4) ?

Optical polyester


Osaka Gas Co. Ltd and Kanebo Ltd have co-developed an amorphous polyester material, OKP-4. It is now available commercially from Osaka Gas Chemical. The characteristics of OKP-4 are as follows:

Having a slightly lower transmittance value (90 % for 3 mm thickness) than cycloolefin polymer (COP), OKP-4 is mainly used for an alternative to this latter in optical system when a higher refractive index is required. Moreover, its Abbe number, quantifying the refractive index change with the wavelength, is relatively low compared to the high value of this index (at a given wavelength). Jointly, its density is 20% more important than Zeonex, and slightly superior to PC’s and PMMA’s.


OKP-4 has very low water absorption, two times less than PMMA and 30% less than PC.  Up to 60°C, it resists fairly well low concentration organic acids and diluted minerals as well as diluted alkaline solutions. Its resistance to diminishing light transmission due to aging is very good. However, as a polyester, it must not be used with the following materials at ambient temperature:

Please refer to the manufacturer or GAGGIONE for a use at a temperature superior or equal to 60 °C, in which case the chemical use is more restrictive.


Like COP, OKP-4 polyester has a low dielectric constant that makes it useable as electric insulating components.


OKP-4 has a relatively low thermal expansion coefficient, comparable as the one of PMMA or Zeonex. As these latter, OKP-4 is combustible and burns without producing an excessive amount of smoke (UL 94 HB). Depending on the particular grade, the glass transition temperature is between 121 and 142 °C. This makes a much more per permissive use of OKP-4 than PMMA, allowing to be used in an environment with a temperature up to 100°C, even more for some grades. This is not the case for PMMA, for which the heat deflection temperature under 1.80 MPa doesn’t go above 100°C, but goes to 123 °C for a grade of OKP-4 (OKP4HT).


OKP-4 is suitable for both vacuum-applied metallization and silk-screening.



The very high fluidity of OKP-4 makes it easy to obtain high performance injection-molded objects and films.


As OKP-4 very well resist to high temperature, machining is feasible on this material (diamond turning for instance).

GAGGIONE, optical solutions manufacturer

We are a plastic lens injection company based in France. With more than 70 years of experience, we cover a wide range of activities including imaging. We use the COP Zeonex for custom imaging projects.