The Practical Difference Between POM-H and POM-C

Acetal is a common engineering thermoplastic also known as polyoxymethylene (POM). It is a semi-crystalline polymer available in two forms:

• POM-H (Homopolymer) — produced by anionic polymerization of formaldehyde, resulting in extensive crystallization; historically branded as Delrin in North America.
• POM-C (Copolymer) — produced by cationic polymerization of trioxane with a small amount of comonomer, leading to a lower rate of crystallization; historically more common in Europe.

POM materials are widely used in semiconductor-processing equipment where a balanced set of properties is required at a reasonable cost. Selecting the optimal version depends on understanding each material’s limitations:

• POM-H offers higher mechanical strength and stiffness thanks to its simpler polymer structure and greater crystallinity.
• POM-C provides superior chemical resistance and steam/hydrolysis resistance up to 185 °F, and is generally lower in cost.
• Center-line porosity in thick POM-H sections can raise outgassing concerns in semiconductor environments.

Side-by-Side Property Comparison

Matching application needs to the right Acetal grade is more important than relying on a familiar trade name. For guidance, consult Port Plastics—your global leader in plastic shapes for semiconductor applications.