NYLON

• Very tough, hard and pretty rigid
• Good Mechanical Strength
• Good impact resistance
• Very good to machine

• Very good wear resistance (esp. gritty environment)
• Good chemical resistance
• Many grades meet FDA reg.
• Cont. use temperature 220°F

• Higher moisture absorption than acetal (Can result in dimensional change of 2%!)
  
• Extruded nylon vs. cast nylon will have more internal stress
  
• A little more difficult to cut and finish as cleanly than acetal

ACETAL
(commonly referred to as Delrin—see our May E-Zine!)

• Low level of moisture absorption
• Very good wear resistance
• Good impact resistance
• High fatigue resistance
• Good resistance to chemicals

• Very stable, rigid and hard
• Very good surface finish
• Many grades meet FDA reg.
• Cont. use temperature 180°F
• Excellent sliding properties

• Not resistant to UV rays, may become brittle
  
• Delrin brand (homopolymer) may have centerline porosity—problem for food and medical applications. Should use Copolymer grade.
  
• Not as good as nylon in abrasive environments

UHMW
(UltraHighMolecularWeight Polyethylene)

• No moisture absorption
• Excellent wear resistance
• Very low coefficient of friction (slick)
• Excellent resistance to chemicals

• Food Safe
• Excellent sliding properties
• LOW COST
• Very good impact resistance

• Low compressive strength—not great wear for heavy loads
• Low temperature resistance—max. continuous use 180°F
• Low coefficient of thermal expansion (dimensional change w/ temperature change)

PET
(known commonly as Ertalyte® *)

• Excellent dimensional stability
• Excellent chemical resistance
• Very low coefficient of thermal expansion
• Can be machined to tight tolerances

• Very good wear resistance
• Very low moisture absorption
• Can sustain high loads
• Cont. use temperature 210°F

• Not the best impact resistance, can be brittle