Plastic density chart: g/cm³ and lb/in³ for 60 resins and filled grades

Density chart: commodity resins

Typical ranges from published producer data sheets, measured at 23°C (73°F). Pounds per cubic inch are g/cm³ × 0.036127. “In water” compares the range with fresh water at 23°C (0.9975 g/cm³); “either” means grades fall on both sides. Your grade’s own data sheet is what counts.

Density chart: engineering resins

Nylon values are dry as molded. Impact modifiers lower density, and flame retardants usually raise it.

Density of glass-, mineral- and carbon-filled grades

Glass fiber is about 2.6 g/cm³, so it adds weight fast: a 30% glass nylon is about 20% heavier than the same unfilled nylon. Fill level matters too. A GF33 or GF35 grade is not a GF30 for part-weight math. See glass-filled plastics for what the glass does to the part.

High-performance resins and fluoropolymers

PTFE and FEP are the densest common plastics, above 2.1 g/cm³. A PTFE part weighs more than twice as much as the same part in PP or PE.

Thermoplastic elastomers

TPE, TPO, TPU and TPC density depends heavily on hardness, oil and filler content, so these ranges are wider than for unfilled resins. Check the exact grade.

How density sets part weight and cost per part

A molded part weighs its volume times the density of the resin. Two resins at the same price per pound do not give the same cost per part: the denser one puts more pounds into every part, so you get fewer parts per pound. The table shows the same 50 cm³ (about 3.05 in³) part in four resins.

• Part weight = part volume × density. In U.S. units, multiply volume in in³ by the lb/in³ value in the charts above.
• Cost per part = part weight × price per pound. Add runner or sprue weight if you do not regrind it.
• Compare prices on a volume basis. Multiply price per pound by density. A resin at 1.20 g/cm³ must cost about 13% less per pound than one at 1.04 g/cm³ to give the same material cost per part.

The molding calculators do this math with your own numbers, and the unit converter handles g/cm³, kg/m³, lb/ft³ and lb/in³. To take weight out of a part, see reduce part weight.

Will it float? The sink-float check

Polyethylene, polypropylene and most olefin elastomers are lighter than water and float. Almost every other unfilled resin sinks. Fillers change this: PP with 20% talc or 20% glass is about 1.03–1.06 g/cm³ and sinks, even though unfilled PP floats. Some TPE and TPO grades straddle 1.00 and can go either way. Nylon 12, at about 1.01–1.02, sinks, but only slowly.

• Quick test. Drop a few pellets in room-temperature water with a drop of dish soap so trapped air does not hold them up. Floating pellets are very likely an olefin; sinking pellets could be almost anything else.
• Limits. Foamed parts and parts with voids can float even when the resin sinks, and the test cannot tell PP from PE. See identify unknown plastic pellets for the next steps.

How density is measured: ASTM D792 and ISO 1183

• ASTM D792. The displacement method: the specimen is weighed in air and then in water (Method A) or another liquid (Method B). The result is specific gravity at 23/23°C. Density in kg/m³ is specific gravity × 997.5.
• ISO 1183-1. Method A is immersion, for void-free solid specimens. Method B uses a liquid pycnometer, for powders, granules and flakes. Method C is a titration method. ISO 1183-2 covers the density-gradient column.
• ASTM D1505. A density-gradient column held at 23°C, used for polyethylene, where small density differences separate grades.

Specific gravity and density in g/cm³ differ by only 0.25%, so a sheet listing a specific gravity of 1.14 and one listing 1.14 g/cm³ agree at that precision. For unit math: 1 g/cm³ = 1,000 kg/m³ = 62.43 lb/ft³ = 0.036127 lb/in³.

Solid density vs. pellet bulk density

The values on this page are solid density, the mass of the plastic itself. They set part weight. Pellet bulk density is a different number: the weight of pellets that fills a given volume, air gaps included. Many unfilled pellets run roughly 30–45 lb/ft³ (480–720 kg/m³) poured, often around half to two-thirds of the solid density, and denser resins run higher: one PET bottle resin data sheet lists a bulk density of 0.86 g/cm³ (about 54 lb/ft³). Bulk density is measured by ASTM D1895 and is used to size hoppers, dryers and gaylord loads, not to calculate part weight. See bulk density of plastic pellets.

Why density varies within one resin

• Filler and reinforcement. Density follows the mix. Unfilled PA66 at 1.13 g/cm³ with 30% glass at about 2.6 g/cm³ gives 1 ÷ (0.30 ÷ 2.6 + 0.70 ÷ 1.13) = 1.36 g/cm³, which matches producer sheets.
• Crystallinity. Amorphous PET sheet is about 1.33–1.34 g/cm³ while crystallized PET pellets are about 1.39–1.40. In polyethylene, branching sets density, which is why LDPE and LLDPE sit below HDPE.
• Additives. Flame retardants usually add weight, so check a flame-retardant grade’s own sheet rather than the standard grade’s. Impact modifiers lower it: Zytel ST801, a supertough PA66, is listed at 1.08 g/cm³ (ISO 1183), against 1.13–1.14 for standard PA66.
• Moisture. Nylon data sheets give density dry. It changes little with moisture, but nylon parts grow as they absorb water.

Common questions

A polymer chemist reviews every request. Send the grade you run now and we will match it or find a qualified equivalent. Orders start at one gaylord.