Couplable means that a large double sleeping bag can be made from two sleeping bags. For this you need a model with a right and a model with a left zipper. Open the zippers on both sleeping bags completely. Now you can connect the zipper from the right sleeping bag to the left. So you get a cozy two-person sleeping bag.
Since the sleeping bag has an all-round zip, there are two triangles around the foot area. The all-round zip isolates much better, but can only be coupled to a limited extent.Tip from the Grüezi bag team:
Since it is usually too warm for two, the zipper should only be closed on the side and left open at the bottom.