A device for folding layer material, the layer material defining layer sections including at least one folded layer section and a connecting layer section laterally directly connecting to the at least one folded layer section, comprises: a device base; a conveying path for conveying the layer material relative to the device base in a conveying direction along a folding path section; and, a folding member including guiding members for longitudinally folding the layer material from an initial layer state to a folded state only within the folding path section while the layer material is conveyed therethrough. The folding path section defines folding path ends including a beginning end where the layer material initially begins to be folded by partly erecting the at least one folded layer section from the initial layer state with respect to the connecting layer section and with respect to the device base, and a finishing end where the layer material reaches and then maintains the folded state. The guiding members deflect the connecting layer section while simultaneously folding the at least one folded layer section to the folded state from the beginning to the finishing ends. A first guide member engages the layer material on a first side and a second guide member engages the layer material on a second side while opposing the first guide member. The first and second guide members are positionally adjustable about a substantially common guide axis. The folding member can comprise a plow folder.