A silver logo on a white T-shirt or a clear TPU badge on a light grey jacket can turn yellowish after a few months in a warehouse or in the sun. On light-coloured products this is one of the more common reasons for quality complaints. This guide explains why TPU film yellows, what to look for when choosing a non-yellowing TPU film, and which tests you can ask for during sample approval.
Why does TPU film turn yellow?
Yellowing happens when new chemical groups form in the polymer and absorb light differently. In textiles there are four main triggers:
- UV light: TPU based on aromatic isocyanates (mostly MDI) photo-oxidises in sunlight and gradually yellows. The tendency comes from the chemistry of the material itself.
- Heat: Pressing hotter or longer than needed, or pressing the same piece more than once, speeds up thermal oxidation.
- Nitrogen oxides (NOx): In warehouses exposed to gas heaters, forklift exhaust or traffic fumes, these gases can cause discolouration.
- Phenolic yellowing from packaging: BHT-type antioxidants in some polyethylene bags react with NOx to form yellow compounds that can transfer to the product. The fabric yellows too, so TPU is not always the culprit.
Dye migration is a related problem that looks similar. On dark polyester fabrics dyed with disperse dyes, high press temperatures can drive dye into a light-coloured film. The result looks alike, but the fix is different.
How to choose a non-yellowing TPU film
- Aliphatic or aromatic? TPU based on aliphatic isocyanates is inherently more light-stable and usually costs more. Confirm which type you are buying on the technical data sheet (TDS).
- Additive package: In aromatic grades, UV absorbers, HALS light stabilisers and antioxidants slow yellowing down but do not eliminate it. Ask which test and exposure time an “anti-yellowing” claim is based on.
- Colour and finish: Yellowing shows up much earlier on white, clear, pastel and metallic silver films; on dark colours the same change often goes unnoticed. Choose the film for the lightest colour in the collection.
- Process window: Even the most stable film can yellow if overheated. Take the temperature and dwell range from the film’s TDS and verify it on your own line.
Tests to request at sample approval
- Colour fastness to light: ISO 105-B02 or AATCC TM16.3, using xenon-arc exposure to simulate daylight.
- UV discolouration: ASTM D1148, used for light-coloured polyurethane and rubber surfaces.
- Phenolic yellowing: ISO 105-X18, which assesses the packaging risk.
- Colour fastness to nitrogen oxides: ISO 105-G01, which reflects gas exposure in storage.
- Measurement and records: Record results with a grey scale or a spectrophotometer (for example the ASTM E313 yellowness index) rather than by eye, and keep an unexposed reference sample.
Which tests you need depends on where the product will be used and on your brand’s specification: light fastness matters most for outerwear, phenolic yellowing for white collections. Storing goods somewhere cool and dark and using BHT-free packaging also lowers the risk.
For general film selection criteria, see the TPU selection guide. For colours and finishes, visit the Premium TPU film page, and to plan these tests alongside wash testing, read the wash durability guide.
Related solutions
This article was summarised and commented on by the LTS Frekans editorial team, drawing on the source article.
