A door, in particular a roll-up door, having a curtain that can be moved between a closed position in which it is arranged, at least in sections, approximately in a plane and an open position in which it is wound, preferably at least in sections, on a winding shaft, said curtain having at least one thermally insulating region such as an insulating body, preferably made of PE foam. The insulating region is formed by a pocket bordered at least partially by strip-shaped, deformable reinforcing layers, in particular made of plastics, particularly preferably made of PVC.