What is POM

What is Polyoxymethylene? (POM)

Updated 17/02/2026

Polyoxymethylene (POM) was discovered by Hermann Staundinger in the 1920's, however the material was thermally unstable so not useful commercially.

Commercialisation followed in the late 1950's/early 1960's when DuPont started to produce Derlin®, its version of POM homopolymer, and Celanese started its production of Celcon®, other manufacturers followed with their own versions of the materials.

Also known as Polyacetal, polyformaldehyde and Acetal, POM is an engineering thermoplastic used in precision parts. It is characterised by its high strength, hardness and rigidity and often used in applications requiring high stiffness, low friction and excellent dimensional stability.

Table of Contents

POM's Unique Crystallinity Gives It Exceptional Dimensional Stability

Moisture Doesn’t Affect Its Dimensions, But It Still Matters

Thermal Degradation Doesn’t Always Show Up as Warping

Excellent Wear and Low Friction But Not Self-Lubricating

Two Structural Forms: Homopolymer vs. Copolymer Matter a Lot

Recyclability Is Better Than Many Engineering Resins

Why This Matters for Design & Manufacturing

Typical Applications

POM's Unique Crystallinity Gives It Exceptional Dimensional Stability

Acetal is a high-crystallinity thermoplastic (~70–80% crystalline), which means its molecules pack very regularly. This high crystallinity:

  • Keeps tight tolerances stable even after machining and thermal cycling.

  • Reduces moisture uptake compared to many other engineering polymers.

  • Helps maintain low creep under load, beneficial for precision gears, bearings, and sliding components.

This is why Acetal is often chosen for precision parts in fluid systems and mechanical assemblies where tight fits are critical.

Moisture Doesn’t Affect Its Dimensions, But It Still Matters

Unlike nylon and some engineering plastics, Acetal absorbs very little moisture (typically < 0.2% at equilibrium). This means:

  • Mechanical properties stay stable in humid environments

  • Dimensional precision is retained even after water exposure

However even small amounts of absorbed moisture can influence mechanical damping and acoustic behaviour, which matters in precision instruments and noise-sensitive mechanisms.

Thermal Degradation Doesn’t Always Show Up as Warping

Acetal tends to thermally degrade by releasing formaldehyde at elevated temperatures rather than soften like many polymers. This means:

  • Parts can look fine but have compromised internal chemistry

  • Overheating during molding/processing can reduce long-term mechanical performance even if part dimensions look acceptable

Proper processing and heat stabilisers are critical to long-term reliability.

Excellent Wear and Low Friction But Not Self-Lubricating

Acetal has inherently low friction and good wear resistance (which is why it’s used for gears and bearings), but:

  • It is not technically “self-lubricating.”

  • In long-life, high-load applications, lubrication or composite fillers (e.g., PTFE) can meaningfully extend life.

Unfilled Acetal tends to perform best in:

  • Oscillating motions

  • Low-to-moderate sliding applications

Two Structural Forms: Homopolymer vs. Copolymer Matter a Lot

Many people know “Acetal or POM” generically, but the homopolymer and copolymer grades behave differently:

Homopolymer (POM-H) FL321

  • Higher stiffness and strength

  • Slightly higher crystallinity

  • Better for machined precision parts

Copolymer (POM-C) FL381

  • Better chemical resistance, especially to acids and chlorinated solvents

  • Lower risk of degradation (e.g., less formaldehyde release under heat)

  • Often more forgiving in injection moulding thin walls

Choosing the wrong form for an application (e.g., homopolymer where a solvent is present) can lead to premature failure.

Homopolymer and Copolymer are available in several reinforce and glass fibre reinforced extrusion and injection moulding grades.

Recyclability Is Better Than Many Engineering Resins

Acetal recycles relatively well compared to some high-performance polymers. Regrind can often be reused in noncritical applications with minimal property loss. This can be a cost and sustainability advantage in high-volume manufacturing. POM applications are 100% recyclable, either as feedstock or mechanically.

Why This Matters for Design & Manufacturing

Acetal is more than just a tough engineering plastic. Its value lies in:

  • Dimensional reliability
  • Low moisture sensitivity
  • Excellent wear and sliding performance
  • Chemical and electrical stability

…but only when matched correctly to application demands and processing variables.

Typical Applications

  • Bushings
  • Seat Belt Components
  • Steering Columns
  • Filter Housings
  • Food Conveyers
  • Fasteners
  • Insulin Pens

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