A sustainable alternative to aluminium

There are multiple considerations when comparing polymer and aluminium windows, especially when it comes to sustainability, performance, and design flexibility. Here, Steve Tonkiss of REHAU addresses the debate head-on.

As we approach government decarbonisation targets for 2030 and 2050, and with the recent introduction of the Future Home Standard, pressure to comply with new regulations for thermal performance and sustainability is mounting. Consequently, more energy-efficient windows consisting of recycled materials are becoming more attractive to homebuilders and developers.

Additionally, raising awareness around the need for sustainable products means consumers’ expectations have changed and they now expect greener options. Scrutiny has therefore increased around window materials.


The sleek, modern-looking finish of aluminium windows may suit certain home styles, but not others. By contrast, polymer is more adaptable for both modern and traditional-looking properties, with indistinguishable wood ‘facsimiles’ and foils in multiple colours available, alongside traditional white.

Additionally, PVCu tends to be more cost-effective – aluminium flush fit casement windows can be up to three times more expensive – and offers greater thermal efficiency, whereas metal’s thermal conductivity leaves windows susceptible to condensation. Though this can be resolved by installing polymer thermal breaks, further issues can arise from incorrect installation.


Aluminium has been recyclable for decades – around 75% of the material ever produced remains in circulation today – and its recycling process uses 5% of the energy that it takes to produce new aluminium, making it sustainable. As it needs to be re-smelted at temperatures above 600°C, aluminium recycling is energy-intensive however, with an average equivalent of 0.5 tonnes of CO2 emitted per tonne of material recycled gate-to-gate. Extraction of raw materials like bauxites – including mining and refining – is also energy-intensive, producing higher levels of CO2.   

The polymer recycling process separates old frames into different materials, creating ‘clean’ PVCu pellets for manufacturing new windows. Because the process is less energy-intensive than aluminium recycling, its carbon footprint is roughly one-fifth smaller. While new polymer production has relatively high embodied carbon, it is less than half that of aluminium.


Millions of new windows are installed in the UK annually, meaning many old frames are scrapped. To reduce the amount of polymer going to landfill, suppliers must commit to the circular economy.

Part of REHAU, PVCR collects and separates polymer windows and door frames, directing recyclable materials back into window manufacturing processes. This reduces polymer going to landfill, enabling a more sustainable business model and products.


Before recycling processes improved, polymer window profiles were primarily manufactured using mono-extrusion methods. Multi-layer co-extrusion instead combines recycled and virgin polymer using two dies concurrently, with window cores being 100% recycled polymer and outer skins made from virgin materials. This enables suppliers to keep valuable raw materials within the circular economy.

Importantly, using recycled polymer in frame cores does not impact window performance. Instead, the aesthetic appeal of virgin polymer is retained alongside durability and thermal efficiency levels.

Currently 55% of salvaged polymer frames are converted into material used in our products. We aim to increase the amount of good-quality polymer being reused to 70% through further enhancing PVCR’s processes.


Housebuilders and developers are mainly familiar with polymer’s green credentials, but suppliers must foster greater awareness and educational opportunities to make recycling the material more commonplace.

The overall aim must be to ensure homebuilders and developers use more recycled polymer windows, and that supply chains provide scrap windows materials, including whole frames and off-cuts, to facilitate this. Partnerships with homebuilders, developers, fabricators and installers to arrange local delivery of scrap polymer for recycling are therefore required.


Attitudes to sustainability are shifting, with homebuilders, developers and consumers concerned about the eco-friendliness of windows, including their use of recycled materials. Traceability can prove a useful tool for housebuilders and developers looking to allay these concerns.

In conclusion, advancing polymer window technology, alongside its ability to realistically mimic aluminium at a more cost-effective price point, has long made PVCu an appealing choice for housebuilders and developers.
This, combined with its significantly lower embodied carbon level and reduced recycling footprint means the material is likely to grow in prominence as sustainability becomes a bigger priority for everyone.

Steve Tonkiss is head of sales (south) at REHAU