- The ProPEX® Engineered Polymer (EP) Elbow makes 90 degree connections for Uponor cross linked polyethylene (PEX-a) tubing for use in hot and cold domestic potable water systems, residential fire safety and hydronic radiant heating and cooling systems. Each end of the elbow is manufactured with an Uponor ProPEX® fitting for connections to Uponor AquaPEX® or Wirsbo hePEX™ tubing.