Produced through free-radical polymerization, LDPE has the most long- and short-chain branching of any form of PE, resulting in its lower density. The branching keeps the molecular chains from packing tightly in its crystaline form, so LDPE has less tensile strength but greater ductility. That exceptional “formability” makes LDPE particularly useful for a range of applications, from rigid products like plastic bottles, buckets and bowls to filmy ones like plastic grocery bags and plastic cling-wrap. Did you have cereal for breakfast? The lining of the milk carton and the plastic bag inside the cereal box were likely made with LDPE. On the opposite side of the polymer chain, we have HDPE, which is characterized by minimal branching of the polymer chain. Less branching means those nicely linear molecules pack together well during crystallization, making HDPE much denser and rigid. That added tensile strength means HDPE is the PE of choice for applications that require a bit more “backbone,” such as milk and detergent jugs, garbage cans, water pipes and children’s toys. It’s also one of the reasons why HDPE has largely replaced cardboard as the tube material of choice in making fireworks. An HDPE tube is less prone to shattering if a firework malfunctions, and once the boom inside the tube is exhausted, the HDPE tube is recyclable.