HDPE pipe for Gravity & Low Pressure Applications Weholite is a large diameter gravity or low pressure structural wall pipe made from special high density polyethylene (HDPE) resin. With Weholite, raw material properties have been combined with advanced product technology to create a lightweight engineered pipe with superior loading capacity. It is used to convey liquids or air, under ground, above ground or under water in low pressure applications up to 2 bar internal pressure.