What is interfacing ? – Where is it used ? and why do I need to use it? Interfacing is an additional layer applied to the inside of a garment or craft project when you want that area to be firmer. With dress making it is adding to certain area’s only, collars, cuff, waistbands and plackets. For craft projects, its added where you need to add firmness or structure. You would use interfacing on button bands. Waist band and front openings need interfacing Cuffs and collars need