Resin identification code - Wikiwand
塑料材质大全（PET/PS/PP/PVC...） - 知乎
软胶制品材料选择——硅胶、TPE、TPU、PVC、橡胶的区别 - 知乎
1: polyethylene terephthalate (PETE) (beverage bottles, cups, other packaging, etc.)
2: high-density polyethylene (HDPE) (bottles, cups, milk jugs, etc.)
3: polyvinyl chloride (PVC) (pipes, siding, flooring, etc.)
4: low-density polyethylene (LDPE) (plastic bags, six-pack rings, tubing, etc.)
5: polypropylene (PP) (auto parts, industrial fibres, food containers, etc.)
6: polystyrene (PS) (plastic utensils, Styrofoam, cafeteria trays, etc.)
7: Other (N/A) other plastics, such as acrylic, nylon and polycarbonate.
As the number increases, the complexity of recycling increases
1 and 2 are mechanically recyclable
「塑膠射出」拿出你的手機檢查一下 小心對 🐤🐤 有巨大影響？【超認真少年】Plastic Injection Phone Case - YouTube
TPU: clear, soft, yellow after UV exposure
Silicon: soft
BPA 雙酚 A : toxic