Short answer
Choose cast nylon for large parts that run under impact and wear; choose POM for small, close-tolerance parts that must hold their size in humid conditions. Cast nylon is better at absorbing shocks and in large sizes, while POM offers low moisture absorption and high dimensional stability.
The key differences
POM (polyacetal) has a density of 1.41 g/cm³ and very low moisture absorption, so it holds its size in close-tolerance gears, bushings and machine parts. Cast nylon can absorb 5.5 – 7 % moisture at saturation, which matters for very tight tolerances on small parts.
In return, cast nylon is tougher under impact and load, highly wear resistant and can be cast in very large sizes. POM is not an economical choice for a large pulley or a thick wear plate.
Which one for which application?
- Crane pulleys, sheaves, large gears: cast nylon.
- Precision gears, small bushings, pump parts: POM.
- Slides, wear plates, conveyor parts: cast nylon.
- Size-critical parts in humid conditions: POM.
We cover gear selection separately in cast nylon gears.
Supply and machining
We supply both materials as sheet, rod or CNC-machined parts. See all options under engineering plastics.
Share your drawing and operating conditions and we can price both materials so you can compare: get material advice.
Frequently asked questions
Is POM stronger than cast nylon?
It depends on which strength you mean. POM is harder and more dimensionally stable; cast nylon is tougher under impact and has the edge in wear on large parts.
Which is used in food machinery?
Both are available in food-grade versions. See engineering plastics in the food industry.
