Polyethylene
One monomer, four very different materials — the difference is how tightly the chains pack. Low-density (LDPE) stays branched and flexible, which is why it becomes film and bags. High-density (HDPE) packs straight and stiff, so it becomes pipe, containers and automotive parts. Linear low-density (LLDPE) trades stiffness for puncture resistance in stretch film, and ultra-high molecular weight (UHMWPE) runs chains so long the material outwears steel in abrasion service.