Acetal is the common name for a family of thermoplastics with the chemical name POLYOXYMETHYLENE, or POM.
Acetal is available in 2 general types of resins:
- Copolymer acetal (POM-C)
- Homopolymer Acetal (POM-H), commonly called Delrin
Acetal mills better at thicker gauges. Center Line Porosity is a problem on thicker Delrin.
Delrin is more porous than Acetal.
An additional difference is the inherit problem of center-line porosity in the homo-polymer grades (Delrin). This is caused by out gassing during manufacturing, and can be found at the center or on the surface of all homo-polymer extrusions. This porosity can cause problems with machining or moisture permeation through the material. The co-polymer resin (Acetal) does not have this porosity issue.
I work for a plastics manufacturer so I guess I cheated on the answer.