Plastic Recycling: Why Are Some Types Harder to Process Than Others?

If you’ve ever wondered why a plastic bottle is widely recycled, but a crisp packet or black takeaway tray often isn’t, you’re not alone. The short answer is that “plastic” is not one material. It’s a wide family of polymers with different melting points, densities, additives, colours, and formats, and recycling systems are built to handle some far better than others. Plastic recycling is often talked about as a simple yes-or-no issue. In reality, recyclability sits on a spectrum. Some plastics are widely recycled and turned back into new products, while others are difficult, costly, or currently impractical to recycle at scale.

In the UK, this distinction matters. Around 2.3 million tonnes of plastic packaging are placed on the market each year, and while recycling rates have improved, only around 51% of plastic packaging is recycled or recovered. The rest is typically sent to energy recovery or disposal routes. That’s progress, but it also highlights a reality: around half still doesn’t become new plastic again, and “hard-to-recycle” formats are a big part of the reason.

So why do some plastics recycle easily while others don’t? The answer lies in material chemistry, product design, contamination, and the realities of recycling infrastructure.

1) Plastic is not one material

The word “plastic” covers a wide range of polymers, each with different properties. These are identified by resin identification codes (the numbers inside the recycling triangle).

Some polymers are far easier to recycle because they:

• Melt at predictable temperatures
• Can be sorted accurately
• Have strong end-markets for recycled material

Generally easier to recycle in the UK:

• PET (1) – drinks bottles and some food trays
• HDPE (2) – milk bottles and detergent containers
• PP (5) – tubs, pots and caps

These plastics benefit from established collection systems and consistent demand from reprocessors.

Other plastics, such as PVC (3), polystyrene (6) or mixed “other” plastics (7), are harder to manage due to additives, density, or limited market demand. When different polymers are mixed together, the quality of recycled output drops significantly.

2) Packaging design can matter more than material choice

One of the biggest barriers to recycling is multi-layer and composite packaging.

To extend shelf life, improve durability, or reduce weight, many products combine multiple layers of plastic or bond plastic with aluminium or paper. These formats are extremely difficult to separate mechanically, which is how most UK recycling facilities operate.

Recycling systems are most effective when materials are clean, consistent and made from a single polymer. Sector insight highlights that mechanical recycling relies on predictable material behaviour, which becomes far more difficult when packaging combines multiple layers or materials. When plastics are designed primarily for performance rather than end-of-life recovery, even well-established recycling infrastructure can struggle to process them efficiently.

This is why packaging design plays such a critical role in determining whether plastic is recycled in practice, not just in theory.

3) Flexible plastics and films create operational challenges

Flexible plastics introduce practical problems at sorting facilities. They can:

• Tangle in machinery
• Be misidentified by sorting equipment
• Contain multiple polymer layers

From an operational perspective, hard-to-recycle plastics often create challenges long before reprocessing begins. Waste-management specialists consistently point to issues such as complex material composition, contamination, and higher processing costs as key barriers to successful recycling. Flexible and composite plastics, in particular, require more intensive handling and are more likely to be rejected if quality standards are not met.

Improving segregation at source remains one of the most effective ways for organisations to increase recycling performance and reduce the risk of material being diverted away from recycling altogether.

4) Colour, additives, labels and glue can stop “good” plastic becoming good recyclate

Even within a single polymer type, packaging can contain lots of extras:

• Colour pigments
• UV stabilisers
• Flame retardants
• Fillers
• Adhesives
• Sleeves and labels

These can reduce the quality of the recycled plastic, limit the applications it can be used for, or create contamination issues.

Why black plastic has been a big issue

Black plastic has been a known UK sorting challenge because traditional carbon-black pigments can make packaging hard for near-infrared (NIR) sorting systems to detect, meaning it can be missed or incorrectly sorted

The key takeaway is simple: even if the polymer is recyclable, design choices like colour and label materials can make it far harder to recover at scale.

5) Contamination is a deal-breaker

Contamination is one of the most common reasons plastic fails to recycle, even when the material itself is “easy”.

Typical causes:

• Food residue (especially oils and sauces)
• Liquids left in containers
• Items put in the wrong bin
• Non-recyclables mixed into recycling

For businesses, contamination can have a direct cost impact. If recycling loads are rejected, they can be diverted to general waste treatment routes instead.

6) UK infrastructure and end markets play a major role

Even with perfect design and perfect sorting, recycling must still be economically viable.

In the UK, packaging waste overall is substantial, and recycling performance varies by material. Defra’s UK waste data reports provisional figures for 2024 suggesting between 64.1% and 75.2% of UK packaging waste overall was recycled (across all materials). Plastic packaging, specifically, has a lower rate, with recent summaries citing around 51% recycled or recovered in 2024 based on Defra’s dataset.

Why the gap?

• Recycling different polymers requires different equipment and processes
• Some plastics have weaker end markets, so there’s less financial incentive to collect and process them
• Collection rules vary locally, which impacts what arrives at facilities in the first place
• Capacity and technology are improving, but investment takes time (the UK is seeing new projects aimed at “closed loop” recycling, particularly for PET trays).

This is also why you’ll see confusion around “recyclable” labelling. What’s accepted can differ by region and by the contracts used by local authorities or waste providers.

What this means for businesses

For organisations generating waste or placing packaging on the market, hard-to-recycle plastics are not just an environmental issue. They affect:

• Waste management costs
• Recycling performance and reporting
• Compliance with evolving UK packaging policy
• Brand and stakeholder expectations

With policy mechanisms such as Extended Producer Responsibility linking costs more closely to packaging recyclability, understanding these issues is becoming increasingly important.

Conclusion

Some plastics are harder to recycle because they were never designed with real-world recycling systems in mind. Others fail due to contamination, complex material combinations, or limitations within current collection and processing infrastructure.

For businesses, improving plastic recycling outcomes starts with understanding what happens after materials leave site. By making informed choices around packaging design, improving segregation at source, and reviewing waste streams regularly, organisations can reduce waste costs, improve recycling performance, and support the transition to a more circular economy.

In many cases, relatively small changes applied consistently can deliver meaningful environmental and operational benefits.