Applied as a coating to many backpacking and hiking fabrics, PU (polyurethane) is a coating that adds a waterproofing layer to fabric, but also reduces tear strength. As the coating is applied to the face of the fabric it’s prone to wear over time, and most PU coatings will offer only moderate waterproofing when new, moving towards water resistance over years of use.

This grid-stop fabric has a very light PU coating on the inside (used for a backpack in this case) to add some level of waterproofing.

Polyurethane Pros & Cons

Coatings are often applied so thin that you can barely tell they’re even there. While newer PEU (polyether urethane) coatings offer additional durability, PU coatings are best treated with care in regards to abrasion, along with proper storage techniques at home, along with allowing gear to fully dry before it’s packed up and stored.

However, unlike silicone treated fabrics PU coatings allow for seam taping. Thus, many tents and waterproof stuff sacks for example, may have a PU coating on the inside to allow for seam taping while providing additional waterproofing, requiring no seam sealing by the end user at home.

Editor's Note: This Jargon installment originally appeared in Issue 58 of TrailGroove Magazine. You can read the original article here.