Home decor glossary: welting
A welt is a covered cord that is sewn into the seam of a pillow or chair cushion. It is used to reinforce the seams but is also decorative. It can range anywhere in size from 1/8′ of an inch in diameter to a chubby 1-2 inches in diameter. The size you choose is determined by the furniture item as well as the look you are trying to achieve.
A self-welt is covered in the same fabric as the furniture piece as seen in this photo of a chair by Christopher Guy. It is often small in diameter and is used not only as a reinforcement but gives the chair or sofa a finished look.
A contrast welt is covered in a fabric different than the body of the furniture. For example, a tan sofa may have a black welt for a graphic look or a solid denim blue sofa may feature a red welt for a casual and fun-loving appearance and also to break up the monotony of one solid color.
A double welt is most often used on formal furniture and provides a detailed, designer look to those pieces.
Welting can also be accomplished through the use of braid, gimp and tape as seen in these pillows by Suzanne Rheinstein for Lee Jofa. It adds an additional detail to your furniture and pillows for that all important designer look.