MDPE sits in the density range between LLDPE and HDPE, and it behaves like the compromise that positioning suggests. It offers better stiffness and moisture barrier than LLDPE while retaining more flexibility, elongation, and impact resistance than HDPE, making it a useful middle option when neither end of the polyethylene spectrum fits the application cleanly.
MDPE shows up most often in applications that need a stiffer hand-feel or better moisture resistance than LLDPE provides, but cannot tolerate the brittleness and tear sensitivity that comes with HDPE. It is a less commonly stocked resin than LLDPE or HDPE, so structures specifying MDPE should confirm lead time and minimum order quantities early in the conversation.