Ash Content
Also called: Ash, filler content, inorganic content
Ash content is the inorganic residue left after burning a plastic sample, used to estimate filler, glass fibre and mineral contamination.
Ash content is the percentage of non-combustible residue left when a plastic sample is burnt in a muffle furnace at high temperature. Because the polymer burns away, the ash represents inorganic material such as calcium carbonate, talc, glass fibre, pigments and dirt. Standard methods include ISO 3451 and ASTM D5630.
Why it matters when buying recycled plastic
- It reveals filler in material sold as unfilled. Filled material is heavier and less tough.
- For glass-filled nylon or PP compounds, ash content gives a practical estimate of glass percentage.
- In washed material, unexpected ash can indicate sand, soil or other contamination.
- Agree a maximum ash level in your purchase order and check it per lot.
How it relates to other tests
Ash content usually tracks with density: a polyolefin that sinks or is unusually heavy often has a high ash result. Together with MFI, these quick tests catch most surprises in recycled lots; see our recycled plastic quality checklist.
A simple furnace test is inexpensive and quick, so it is worth running on every new supplier and periodically on regular deliveries.