MDPE sits in the density range of roughly 0.926 to 0.940 grams per cubic centimeter, placing it between LLDPE and HDPE on the polyethylene density spectrum. Like LLDPE, it is generally produced as a copolymer with controlled short-chain branching, but with less comonomer than LLDPE, giving it more crystallinity and stiffness than LLDPE while retaining more toughness and impact resistance than HDPE.
This middle-of-the-road balance makes MDPE useful in applications that need more rigidity than LLDPE can offer but can't tolerate the brittleness and tear sensitivity that comes with HDPE at thin gauges. It shows up in shrink film, some heavier-duty grocery and merchandise bags, and certain gas and water pipe applications outside of film, where its combination of stress crack resistance and impact strength is valued.
In blown film specifically, MDPE is less commonly used as a standalone resin compared to LLDPE or HDPE, but it does appear as a blend component or in specific structures where a converter wants stiffness gains over LLDPE without giving up as much toughness as a full switch to HDPE would cost them.
Glossary
MDPE (Medium-Density Polyethylene)
A polyethylene resin with density between LLDPE and HDPE, offering a balance of stiffness and toughness, commonly used in bags and protective packaging.
Example
A converter trying to add body and stiffness to a bag structure without losing too much puncture resistance might blend in MDPE rather than switching the base resin entirely to HDPE.
Nuance
MDPE is sometimes overlooked entirely in film conversations because LLDPE and HDPE get most of the attention, but it's a genuinely distinct resin category with its own density range and property profile, not just a 50/50 blend of the other two. True MDPE resin grades are manufactured and sold specifically as medium-density polyethylene.