How we sort plastics

Most plastic products are not correctly labelled, making it difficult to identify their polymer type.

To sort plastics effectively, we rely on:

Polymer characteristics – Understanding the unique properties of each plastic type, such as flexibility, texture, and strength.
Common products – Recognising which everyday items are typically made from specific polymers (e.g., water bottles are usually PET, detergent bottles are often HDPE).
Visual and audio cues – Observing colour, transparency, and surface texture, and using the “snap” or “bend” test to determine plastic type.

Sorting plastic correctly improves recycling quality, reduces contamination, and helps create stronger, more durable products.

Common products: Food packaging, shopping bags
Ease of sorting: Medium
Characteristics: Flexible, soft
Variations: LLDPE – super hard polymer found in water tanks, cooler boxes, traffic cones, trash bins

Key things to remember when sorting plastics

PET and PP thermoforms look similar – You can tell them apart by their sound when tapped or dropped.
PP and LDPE are both used for food packaging – Differentiate them by texture and noise:
- PP (e.g. sweet wrappers, bread bags) has a rough texture and makes a loud crinkling sound when scrunched, like brown leaves under your feet.
- LDPE (e.g. shopping bags, salt packets) feels softer and makes little noise when crumpled, like green leaves in a tree.
Bottle tops are mostly PP and HDPE – Sorting them takes too much time, so we process them together.
Some items contain high levels of additives/fillers –
- Oil jerricans (HDPE), plastic chairs (PP), and crates (PP) often have calcium carbonate fillers.
- These must be processed separately to avoid weakened final products.
Black HDPE and PP may be made from mixed recycled plastics –
- Black plastic is often a result of mixing and recycling many different colours.
- It can contain multiple polymer types, which may reduce quality and make flakes less valuable in the market.

Proper sorting helps protect product quality, reduce contamination, and improve market value.

If all else fails, how about using oil, glycerin, water and alcohol to help you sort?

Try placing a small piece of plastic into different liquids to see how it behaves.

In addition to sorting plastic by polymer type, we also separate it by colour.

This takes extra time, but it helps maintain the original properties of the plastic, making the recycled material more predictable and useful.

Colour affects plastic quality – Some colours have more additives than others, which can change how plastic melts, bonds, and hardens after recycling.
Bright-coloured plastics contain more additives – This can affect processing and the final product’s strength and durability.
Mixing colours creates lower-value material – Black plastic is often made from many mixed colours, which can lead to lower-quality flakes and fetch a lower price in the market.

By sorting plastics by colour, we can produce higher-quality recycled materials and avoid unexpected issues during processing.