When construction is carried out with an exterior window type folding door, the lower rail is designed and manufactured differently than the normal folding door.​

On rainy days, the lower rail is constructed with different external containment methods on the outside and inside of the lower rail to prevent rain from entering the room. The external containment method is a structure in which the outer lower layer surface is raised to the lower part of the folding door, and blocks rain or snow from penetrating into the lower rail to prevent it from entering the room.With this structure, folding doors can be used without any inconvenience even through windows.

Folzen Korea's folding door, which has a test report of insulating folding doors according to glass specifications, helps to maintain indoor temperatures by preventing bad weather from entering the store on hot summer and cold winter days.