Material guide
PET, polyethylene terephthalate
It brings the PET bottle to mind, and that is not wrong. This is polyester, but for industrial use. Hard, dimensionally stable and easy to turn to dimensions that hold, a good value choice when you want stiffness and abrasion resistance in a mechanical part.
What it is
PET, polyethylene terephthalate, is the same polyester family as the bottle in the fridge, but in an engineering grade and in thick semi-finished stock instead of thin blow molded packaging. As an engineering material it sits between POM and PA: harder and stiffer than polyethylene, more dimensionally stable than nylon because it takes up considerably less moisture. It gives a hard, glossy surface that turns and mills nicely, and the dimensions stay put afterwards. Count on PET when you want a stiff, abrasion resistant precision part without moving up in price to an engineering specialty plastic.
Properties
High stiffness and hardness, carries load without deforming
Takes up little moisture and holds its dimensions over time
Good abrasion resistance, stands up to wear in moving parts
Hard, glossy surface that gives tight tolerances in turning and milling
Good dimensional stability compared with nylon in a damp environment
Common applications
PET shows up in plain bearings, slide rails, rollers, gears, washers and precision parts where stiffness and dimensional accuracy are needed. When a designer wants something harder and more dimensionally stable than POM, or is looking for an alternative to nylon that does not swell with moisture, PET is often the answer. It is also used for wear parts and guides in machine building where a glossy, hard surface is an advantage.
Limitations
PET is not a high-temperature plastic, and it is more brittle than the tougher engineering plastics, so for parts that have to take knocks and blows in the cold, nylon or PC suits better. The chemical resistance to strong acids and bases is limited; that is where a fluoroplastic like PVDF or PTFE belongs. The material is not grateful to glue either, so count on mechanical fasteners.
Our PET grades take 110 °C in continuous service and 170 °C for short periods, go down to -20 °C and melt at 252 °C.
Grades and variants
PET is sometimes marketed under several designations, but in semi-finished stock it is the hard, semi-crystalline grade you usually meet, the one described above. The differences between the variants come down to how the material is made and which additives are in it.
Base grades
- PET, the most common grade in semi-finished stock. Hard, stiff and dimensionally stable, for mechanical precision parts.
Additives and reinforcements
- Filled and modified grades, with for example a lubricant additive for even better glide or improved abrasion resistance in bearings and slide rails.
PETG, polyethylene terephthalate with glycol, is its own and softer material in the aesthetic tier, not a PET grade. Do not mix them up.
Machining
PET saws, mills, drills and turns and gives a fine, glossy surface. It is more brittle than the tougher engineering plastics, so avoid knocks in the cold and go easy on hard clamping.
Formats we can supply
PET comes as sheets, round rods and hollow bars, plus film in thinner dimensions. You see formats and dimensions in the range. Want a piece cut to size? Put the measurements into VisualCutter and you see the price straight away.