Clear iPhone cases turn yellow mainly because the TPU they’re made from breaks down under UV light, and heat, skin oils and sunscreen speed that up. Once the plastic itself has changed colour, cleaning won’t reverse it. But if your case looks dingy rather than truly yellow, surface grime may be the cause, and that can be cleaned. In Australia, strong UV and hot cars make this even more common.
The reason most clear cases turn yellow is that they are made from low-grade TPU – thermoplastic polyurethane, which is more susceptible to degradation from UV light than many other materials. Cases made from UV-treated TPU or polycarbonate plastic with TPU edges are less likely to change colour.
You may have noticed a clear case belonging to a friend turning yellow after only a few months; it only takes a short time in the sun to change the colour of most clear plastics. Here is everything you need to know about why clear cases turn yellow and how to avoid it.
The Science Behind Yellowing Clear Cases
As mentioned above, most clear iPhone cases are made from TPU plastic. It is generally a cheap and flexible material that is resistant to impact but usually doesn't stand up to the sun. Most low-end clear cases are yellow for two reasons:
TPU UV Degradation
Sunlight carries rays. Ultraviolet rays have the power to split the bonds inside plastic such as TPU. This splitting is called TPU UV degradation. When plastic is hit by light, it breaks into pieces. Those pieces can mix with oxygen. Forming a chemical called quinone‑imide. Quinone‑imide loves light and absorbs it strongly, which makes the plastic appear yellow. A 2009 study in the journal Polymer Degradation and Stability reported that quinone‑imide is a chromophore, meaning it is a pigment that absorbs particular wavelengths of light.
Think of an old newspaper left on a windowsill. The paper yellows because light changes it chemically, not because it’s dirty, and no amount of wiping brings the colour back. A UV-damaged TPU case works the same way.
Skin Oils, Sweat, and Common Skincare Products
It's a fact that your skin produces natural oils. Your skin also produces sweat, and you expose your phone to other products like sunscreen, hand cream, and sanitisers throughout the day. Soft plastics such as TPU have a rough surface on a microscopic level, which causes them to absorb some of these products. The combination of absorption and heat accelerates the degradation process significantly faster. To learn more about the effects of heat on iPhone cases, check out our phone case extreme temperature guide.
Thus, a clear iPhone case exposed to both sunlight and your body heat has the highest chance of yellowing in the next few months. To avoid yellowing, store your iPhone in a cool and dry place when not in use and clean your iPhone case periodically to remove any impurities.
Not All TPUs Are Created Equal
As explained above, most clear cases are made from TPU plastic. This type of plastic is usually flexible and affordable but may degrade quickly when exposed to sunlight. Other clear cases are made from polycarbonate plastic or have a polycarbonate back plate and TPU edges. However, TPU plastics come in different qualities, some of which yellow faster than others. For instance:
Most cheap clear cases are made from aromatic TPU, which yellows faster when exposed to UV light than aliphatic TPU. Here's a breakdown of the differences in the materials:
| Material Type | TPU UV Exposure | Case Material Feel | Most Common Use |
|---|---|---|---|
| Standard TPU | Yellow after a few months of UV exposure | Flexible and Bendable | Most cheap clear cases |
| UV-Treated TPU | Slower rate of yellowing than standard TPU | Flexible and bendable | Clear bumpers |
| Aliphatic TPU | TPU that is less likely to yellow from UV exposure | Flexible and bendable | Expensive clear cases with clear ends |
| UV-Treated Polycarbonate | Much slower to yellow under UV exposure | Hard plastic | Used in clear backplates (structural or protective plate underneath or forming the rear of the phone) for hybrid cases |
As discussed, most clear cases turn yellow when they are exposed to UV light because of the type of plastic that is used. For example, inexpensive clear cases are made from aromatic TPU, a type of plastic that turns yellow more quickly when it is exposed to UV light. However, iPhone case makers can treat TPU plastic to make it more resistant to UV damage. Some other companies use polycarbonate plastic to make iPhone cases that rarely turn yellow even after being exposed to UV light. However, this does not mean that the cases are completely safe from the effects of UV light.
Why Clear iPhone Cases Turn Yellow: Can Yellow Clear Cases Return to Clear?
Unfortunately, you cannot return a yellowed case to its clear state. The yellowing process involves the breaking of bonds in the plastic, which means you cannot fix it by cleaning the case. Also, using cleaning products such as bleach can damage the case. Make it look cloudy. However, you can take steps to make sure that your clear case does not turn yellow:
- Keep your iPhone away from sunlight, especially in hot areas or when you are storing it in a car.
- Wash your hands before touching your iPhone after using skincare products
- Wipe your case regularly with a soap solution and dry it.
- Remove your case occasionally to prevent product buildup on the surface.
For complete care instructions, check out our guide on how to clean a clear iPhone case without damaging it.
How an Anti-Yellowing Clear Case Is Made
Companies generally use two materials to make high-quality clear cases that resist yellowing. The first is a polycarbonate backplate that resists UV degradation, and the second is Bayer-grade TPU edges that absorb impacts.
Hybrid clear case construction: a UV-stabilised polycarbonate back keeps the panel clear, while TPU edges with UV stabilisers absorb impact.
Bayer Grade TPU Edges
Your iPhone case edges take the most impact when dropping your iPhone, and as such, you need a flexible yet durable material to make them. iPhone case makers use TPU for the edges because it flexes and recovers when your iPhone is dropped. Higher-quality cases add UV stabilisers, which are additives that absorb UV light before it can damage the polymer chains. The edges may still discolour slowly over time, but stabilised TPU holds up much better than untreated TPU.
UV Resistant Polycarbonate Backplate
Most people prefer a clear phone case because of the aesthetic appeal. The backplate of the case is the most prominent clear part, and as such, it needs to resist UV exposure. Manufacturers use a polycarbonate backplate to make sure that the clear part of the case maintains its clarity for a long time. Polycarbonate (PC) is a tough plastic used to make many safety items, including glasses and headlamp covers. However, just like other plastics, PC (polycarbonate) can also yellow when exposed to UV light. A research paper published in the Journal of Failure Analysis and Prevention in 2020 concluded that untreated polycarbonate tends to yellow when exposed to UV light. However, manufacturers can treat PC to improve its UV resistance significantly. We at Sleek Cases offer iPhone cases with a PC backplate with UV stabilisers to make sure that the clear part of your case lasts longer.
The hard back plate also resists the absorption of skin oils, which means it is less likely to yellow compared to TPU. To learn more about the differences between polycarbonate and TPU, check out our polycarbonate vs TPU guide.
What to Look Out for When Buying an Anti-Yellowing Clear Case
Most companies advertise their products as anti-yellow but don't specify what prevents their cases from yellowing. Here are some of the things to look out for when shopping for an anti-yellowing clear case:
- Check the material that makes up the back of the case. A polycarbonate backplate is more likely to resist yellowing than a TPU backplate.
- Look out for cases that mention UV stabilisers or aliphatic TPU as the materials used.
- Check if the material manufacturer has been named. Most materials have technical specifications available online, so you can research them independently.
- Be wary of companies that claim their cases are unyellowable or permanently clear.
If you're looking for a case that offers both UV resistance and good drop protection, check out our Sleek Cases range to view our current stock.
Conclusion
This article, 'Why Clear iPhone Cases Turn Yellow', explains that it happens because they are made from standard TPU plastic, which is susceptible to UV degradation. Moreover, the yellowing process accelerates when the case is exposed to body oils and heat. The changes that cause yellowing occur deep in the plastic material, meaning you cannot remove them by cleaning the case. The best way to ensure that your case doesn't yellow is by choosing materials that resist UV degradation. Sleek Cases offers PC backplate cases that resist UV exposure and Bayer-grade TPU edges that offer good drop protection. When selecting a case, ensure that it is made from materials that resist UV degradation and have been treated to resist UV exposure. Use the checklist above on what to look out for when buying an anti-yellow clear case.
Sources and Further Reading
- Rosu, D., Rosu, L. and Cascaval, C. N. (2009). IR-change and yellowing of polyurethane as a result of UV irradiation. Polymer Degradation and Stability.
- Covestro: Material selection and their chemical properties (TPU)
- Redjala, S. et al. (2020). UV Aging Effects on Polycarbonate Properties. Journal of Failure Analysis and Prevention.
