Denier, often abbreviated as “d” or “D”, is a unit of measurement that is used to describe the thickness of individual fibers or threads. When shopping for backpacking gear or clothing, you’ll often see 10d or 20d tacked onto the end of a specification for the gear’s fabric. Higher denier fabrics are usually heavier and more durable than lower denier fabrics. For example, a quilt with a 10d shell fabric will be slightly lighter weight and less durable than one made with a 20d fabric.