Stretch denim is cotton denim woven with a small proportion of an elastic fiber, most commonly elastane, blended into the yarn. This addition lets the fabric extend under movement, such as bending the knee or sitting down, and then return closer to its original shape once the movement stops.
For you as a wearer, this generally means more comfort and a closer fitting cut feels less restrictive, which is part of why stretch denim is common in skinny and slim fitting jeans. It comes at a small tradeoff: stretch denim tends to fade less dramatically than rigid denim, and the elastic fibers mean the fabric may sag slightly over the course of a day, sometimes called bagging out, before recovering after washing.
Stretch content and construction vary a lot between garments, from a very light touch of stretch to noticeably elastic fabric. See our stretch versus rigid guide for how to choose, and the entry on comfort stretch for a common lighter stretch category.
