Plastic Density Chart: Compare Common CNC Machining Materials

Assorted CNC plastic stock billets labeled by polymer density for comparison

Quick answer

Density (g/cm³) lets you estimate finished part weight, compare stock cost drivers, and spot filled grades. It does not equal strength. Use this chart with mechanical and thermal requirements—not as a standalone selection rule.

When RFQs ask for “lightest possible” or shipping weight is part of the business case, density is the first filter. It also explains why a glass-filled nylon blank feels heavier than the unfilled cousin sitting next to it on the rack.

Why Density Matters in CNC Work

Weight targets for robotics, aerospace, and handheld devices
Rough material cost checks (price/kg × density × volume)
Fixture and dynamic load estimates on moving assemblies
Quick screening for mineral-/glass-/carbon-filled compounds

For filled systems, also read how UHMW-PE and HDPE diverge in wear parts—both are polyethylene-family materials with similar density but very different wear life.

Plastic Density Chart (Typical Unfilled / Common Grades)

Material	Approx. density (g/cm³)	CNC selection note
PP	0.90–0.91	Light; soft machining behavior
HDPE	0.94–0.97	Light tanks, guides, low-load parts
UHMW-PE	0.93–0.94	Light + outstanding abrasion resistance
Nylon PA6/PA66	1.13–1.15	Heavier when conditioned; dry vs wet size
POM	1.41–1.42	Dense for an engineering plastic; stable
PET	1.37–1.40	Precision structural
PC	1.19–1.20	Impact housings; watch stress cracks
PMMA	1.17–1.20	Optical; brittle chip
PVDF	1.76–1.78	Heavy; chemical systems
PTFE	2.14–2.20	Heavy; seals/liners
PPS	1.35 (unfilled) / higher filled	Check filler % on cert
PEEK	1.30–1.32 (virgin)	Filled grades climb quickly

Density vs Strength—Do Not Confuse Them

Heavier is not automatically stronger. PTFE is dense and soft; POM is denser than nylon yet often preferred for precision because of moisture stability, not because density equals modulus. Pair this chart with POM vs nylon performance trade-offs and thermal data from the melting point chart.

Using Density on Real Quotes

Estimate volume from CAD (or bounding box × buy-to-fly factor for plate jobs).
Multiply by density for mass; multiply by price/kg for rough material $.
If weight is critical, challenge metal-to-plastic conversions with real density—not “plastics are light” folklore.
If the cert shows density far above the unfilled range, ask what filler is present before locking feeds/speeds.

Shop tip: A density jump of 0.2–0.4 g/cm³ on a “nylon” blank often means glass or mineral fill—expect more tool wear and different warpage.

Filled Grades and Density Surprises

Glass-filled nylon or mineral-filled POM can sit well above the unfilled density band. Carbon-filled PEEK is denser than virgin PEEK and machines more abrasively. When a purchasing description only says “nylon,” ask for the grade code and density from the mill cert before you lock stock thickness and feeds.

Quick weight estimate

Mass (g) ≈ volume (cm³) × density (g/cm³). For plate jobs, include buy-to-fly: a 200×100×20 mm blank is 400 cm³ before features. At POM ~1.41 g/cm³ that blank is ~564 g before machining—useful for shipping and for checking whether a “lightweight” request is realistic.

Frequently Asked Questions

Why is PTFE so heavy?

Fluorine content and structure drive high density. Useful for some applications; a drawback when weight is the KPI.

Is UHMW lighter than HDPE?

Typical densities are close; UHMW is chosen for wear/impact, not a big density win.

Does PEEK’s density change with carbon fill?

Yes—carbon- and glass-filled PEEK grades are denser than virgin. Confirm the datasheet for mass-critical designs.

Conclusion

Keep a density chart next to your tolerance and temperature notes. It speeds quoting, prevents surprise shipping weights, and flags filled stock early. Then finish the selection with mechanics, chemistry, and machinability—density is necessary context, not the whole decision.