Why TPU cases become yellow? There are two reasons for it. First is the ultraviolet rays of the sun (or sunlight) and the second is the heat from it. These two reasons cause a chemical reaction in the chemical structure of TPU, changing the color. Since this is a chemical reaction, no bleach or soap can remove this yellow color. There are some cases with a composite material that do not turn yellow. But the cheap TPU cases will turn yellow.
Summary
Silicone material cases are soft to touch, very thin and flexible, contouring the body of the phone. This flexibility and softness add to the grip and feel of the phone while not adding to the bulk of the phone. There are some cons to this material as well. It is bad at protecting the devices from shock and is itself poor at scratch, cut, or friction resistance.
Polycarbonate or PC is engineered plastic with great strength but it is brittle. This makes it a bad choice for mobile phone cases. Hence, TPU acts as a hybrid of silicone and polycarbonate. TPU stands for thermoplastic polyurethane. It is both hard and soft, transparent, and good at scratch, shock resistance. It is cheap to produce but turns yellow due to sunlight exposure. This was all about TPU material and silicone. We hope this article helped you understand the difference better.