LDPE (Low-Density Polyethylene)

LDPE is produced through a high-pressure free-radical polymerization process that creates a highly branched molecular structure, with long and short side chains attached to the main polymer backbone. Those branches prevent the polymer chains from packing tightly together, which is why LDPE has a relatively low density, typically in the range of 0.910 to 0.940 grams per cubic centimeter, and why it stays soft, flexible, and optically clear compared to more linear forms of polyethylene.

In film applications, LDPE is prized for its excellent heat sealability, good clarity, and softness, making it a workhorse resin for products like bread bags, sandwich bags, shrink film, and many lamination and coating layers in multilayer structures. It generally has lower tensile strength and lower puncture resistance than LLDPE, which is one reason many film structures today blend LDPE with LLDPE or use LLDPE alone where strength is the priority and LDPE where seal performance, clarity, or softness is the priority.

LDPE was historically the first major polyethylene resin used in blown film and remains widely available and well understood from a processing standpoint, which keeps it a cost-effective, reliable choice for sealant layers and general-purpose film even as newer resins have captured share in structural layers.

A sealant layer in a coextruded bag structure is frequently specified as LDPE or an LDPE blend, since it seals reliably across a wide temperature window even when the rest of the structure uses tougher resins like LLDPE for puncture resistance.

LDPE is sometimes lumped together with LLDPE simply because both start with the letters L-D and L-L-D, but they come from different polymerization processes and have meaningfully different branching structures, densities, and mechanical properties. They are not interchangeable, and a spec written for one cannot be assumed to perform the same with the other.