Engineering Plastics Comparison — Properties of Nylon, Delrin, PEEK, PC & More

Choosing the Right Engineering Plastic

Engineering plastics bridge the gap between commodity plastics (like polyethylene) and metals. They offer strength, wear resistance, chemical resistance, and dimensional stability that commodity plastics can’t match — at a fraction of the weight and cost of metals.

Properties Comparison Table

Property	Nylon 6/6	Delrin (POM)	PEEK	Polycarbonate	UHMW-PE	Acetal Co.
Tensile (ksi)	12	10	16	9.5	5.8	8.8
Flexural Mod (ksi)	410	450	580	345	110	375
Max Temp (°F)	250	220	500	270	180	220
Moisture Absorb	High (2.5%)	Low (0.2%)	Low (0.5%)	Low (0.15%)	None	Low (0.2%)
Wear Resistance	Excellent	Excellent	Excellent	Fair	Outstanding	Excellent
Chemical Resist	Good	Good	Excellent	Fair	Excellent	Good
Machinability	Good	Excellent	Good	Good	Good	Excellent
FDA Approved?	Some grades	Yes	Yes	Some grades	Yes	Yes
Cost (relative)	$	$$	$$$$	$$	$	$$

When to Use Each Material

Nylon 6/6 — The Workhorse

Best all-around engineering plastic. Excellent wear resistance, good strength, self-lubricating. But — it absorbs moisture (up to 2.5%), which causes dimensional swelling. Not ideal for tight-tolerance parts in humid environments.

Gears, bearings, bushings, wear strips
Rollers, pulleys, cable guides
Structural brackets (where weight matters)

Delrin / Acetal (POM) — The Machinist’s Choice

Machines beautifully, holds tight tolerances, excellent fatigue resistance. Low moisture absorption means it stays dimensionally stable. The go-to replacement for Nylon when dimensional stability matters.

Precision gears, cams, linkages
Pump and valve components
Food-contact conveyor parts
Spring elements, snap fits

PEEK — When Nothing Else Works

The Ferrari of engineering plastics. Works at 500°F continuous, resists nearly all chemicals, sterilizable, FDA/medical grade available. Used when you need plastic properties in extreme environments. Expensive — $500+/sheet.

Medical implants and surgical instruments
Aerospace brackets and bushings
Oil and gas downhole tools
Semiconductor wafer handling

Polycarbonate (PC) — Impact & Transparency

Nearly unbreakable — 250× stronger than glass. Optically clear. The material behind safety glasses, machine guards, and bulletproof glazing.

Machine guards and safety shields
Lighting lenses and diffusers
Electrical enclosures
Prototype housings

UHMW-PE — Ultimate Wear & Low Friction

Lowest coefficient of friction of any solid plastic. Self-lubricating, food-safe, chemical-resistant. Weak in terms of strength and temperature, but unbeatable for wear surfaces.

Conveyor guides and wear strips
Chute liners (bulk material handling)
Dock bumpers
Food processing equipment

Metal-to-Plastic Conversion Guidelines

Increase wall thickness: Plastics are 1/3 to 1/60 the stiffness of steel. To match stiffness, increase wall thickness significantly or use ribs.
Add ribs, not wall thickness: A thin wall with ribs is stiffer and lighter than a thick solid wall.
Account for creep: Under sustained load, plastics slowly deform. Reduce design stress to 25–50% of short-term values for long-term loading.
Temperature derating: Plastics lose strength rapidly above room temperature. Check material datasheets for elevated-temperature properties.