What does '600D' mean and does it matter?

600D refers to the denier (thread density) of the polyester fabric; higher numbers generally mean thicker, more tear-resistant material. Specialist-subreddit reviewers note that some Amazon listings overstate their denier, so brands like DEK and Unicook get praised specifically for using the polyester weight they advertise. For most climates a genuine 600D cover with a waterproof coating is plenty; very wet or sun-baked regions benefit from heavier fabric plus UV inhibitors.