POM (polyoxymethylene, also called acetal) is a semi-crystalline engineering thermoplastic built on a -(CH2-O)n- backbone; SpecialChem's 2025 POM guide breaks commercial grades into three families: standard/unreinforced, reinforced, and specialty performance grades [S1].
Within those families, the resin splits at the molecular level into homopolymer (POM-H) and copolymer (POM-C) variants with different stability, chemistry, and processing behaviour, which is the first design decision an engineer makes on a spec sheet [S1]. For context on where POM sits inside the wider engineering-plastics landscape, see the engineering plastics selection map.
Homopolymer vs Copolymer: The Molecular Fork
Homopolymer POM is produced from a single formaldehyde-derived monomer, giving a continuous -(CH2-O)n- chain; this tight chain structure raises crystallinity and delivers higher tensile strength and a higher melting point than the copolymer grade [S1].
Copolymer POM is built by copolymerizing 1,3,5-trioxane with a small fraction of a comonomer (typically an ethylene oxide or dioxolane-type unit) that inserts C-C bonds at intervals along the chain; those C-C bonds stop the "unzipping" thermal-degradation pathway, so copolymer grades hold up better in hot water, hot air, and alkaline environments [S1]. Homopolymer grades tend to be specified where maximum mechanical strength and higher continuous-use temperature are wanted, while copolymer grades dominate food-contact, hot-water, and chemical-exposure service.
Standard and Unreinforced Grades
Standard (neat, unreinforced) POM grades are the baseline resins sold in unfilled pellet form; the guide lists them as a distinct class with the general-purpose property balance of low friction, high stiffness, and good dimensional stability that POM is bought for [S1].
Unfilled POM typically has a density in the 1.41–1.42 g/cm³ range, a melting point around 165–175°C for copolymer and roughly 175–181°C for homopolymer, and a continuous-use temperature that sits near the upper end of the engineering-thermoplastics band. Because the article scope is polymer grades, the POM encyclopedia entry covers the full property set.
Reinforced and Filled Grades
Reinforced POM grades are loaded with glass fibre, carbon fibre, or mineral fillers to lift tensile strength, stiffness, and creep resistance; the SpecialChem guide explicitly names "high tensile strength" as the target property of the reinforced family [S1].
Glass-fibre reinforcement at 20–30 wt% is the most common specification; carbon-fibre-filled grades are used where higher modulus and static dissipation are wanted, and PTFE or silicone-oil-filled grades sit in the friction/wear family discussed next. Each addition shifts shrinkage, density, and mould-shrinkage anisotropy, so moulders usually quote flow and shrinkage data from the specific filled grade rather than neat resin.
Specialty Grades: Friction, Wear, UV, and Food Contact
Beyond the standard and reinforced families, the POM guide lists specialty grades tuned for tribology, UV stability, and FDA food-contact compliance; these are the grades engineers reach for when neat POM misses one specific application axis [S1].
Lubricated / low-friction grades are internally lubricated with PTFE, silicone oil, or MoS2 to drop the coefficient of friction and reduce wear against steel or polymer counterfaces, which is why POM is widely used in conveyor links, gear teeth, and snap-fit bearings. UV-stabilized grades add carbon black or HALS packages for exterior service, and FDA / EU 10/2011-compliant grades are specified for repeated food-contact parts such as metering-gear housings and beverage-dispensing components. Many of these parts end up in conveyors and fillers on packaging machinery lines, where POM's combination of stiffness and lubricity is the deciding factor.
Selection Criteria: Matching Grade to Service
Selection starts with thermal and chemical exposure: hot water, steam, or alkali pushes the choice toward POM-C copolymer; high mechanical load at moderate temperature favors POM-H homopolymer [S1].
The next filter is dimensional and stiffness: if mould-shrinkage warpage and creep under load are the failure modes, a 20–30% glass-fibre reinforced grade is the default. The third filter is the tribological axis; sliding contact against metal at PV values beyond the capability of neat POM calls for a PTFE- or oil-lubricated specialty grade. The fourth is regulatory: food-contact, drinking-water, or medical service forces an FDA / EU 10/2011 / USP Class VI cleared grade. Compared on the four most common decision axes:
Neat homopolymer: highest tensile and stiffness, lowest continuous hot-water resistance. Neat copolymer: best hot-water and chemical resistance, slightly lower strength. Glass-fibre reinforced: highest modulus and creep resistance, with anisotropy in shrinkage. Lubricated specialty: lowest coefficient of friction and wear, at the cost of some tensile strength.
Standards, Designations, and Sourcing Anchors
The resin family is designated "POM" under ISO 1043-1, which is the short code that appears on datasheets and the >PA< POM< recycling triangle; the homopolymer/copolymer split is a property designation, not a separate ISO code.
For procurement, the ASTM D6778 / D6779 POM classification and ISO 9988-1 / ISO 1043-1 are the references that anchor property data, and food-contact service is typically called out to FDA 21 CFR 177.2470 or EU Regulation 10/2011 on the datasheet itself. Major commercial homopolymer families include DuPont Delrin, while copolymer families include Celanese Celcon, BASF Ultraform, and Asahi Kasei Tenac; this list is for reference only, since grade-by-grade qualification against the application requirements always overrides brand choice.
For component-level specifications, see construction machinery and equipment, and lamps and light fittings.