- To control stretch in the entire garment or in those portions of the garment which must withstand the greatest stress as the garment is worn.
Therefore, loosely woven fabrics need interfacings in certain portions and underlinings in the entire garment and the need for supporting fabrics is greater if loosely woven fabrics are used for close fitting garments. Depending on the design a loosely woven fabric may or may not require a supporting fabric throughout the entire garment.
- To add extra body to the fabric of the entire garment for additional weight that will enhance the character of the fabric.
By using underlinings of various weights, the hand and character of a fabric can be altered so that its uses can be extended and multiplied.
For eg; A light weight wool, too light for use in a jacket can be transformed with the addition of an appropriate supporting fabric into suitable fabric for a dress maker jacket.
- To add extra body or stiffness to certain portions of the garment.
Cuffs, stand-up collars, belts, waistbands, pocket flaps and band trims are examples of design units which require interfacings to produce the flat stiff character expected of them.
- To enhance sheer and lacy or open fabrics.
An extra layer of underlining fabrics adds body, enhances colours (a coloured supportive fabric is used) and allows these revealing fabrics to be used for a greater variety of costumes.
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To add body and stiffness to support unusual and exaggerated silhouette lines. A collar with an exaggerated stand, a skirt with molded, rounded hips and a bustle are examples of design features which require foundations of supporting fabric to maintain silhouette lines.
- To act as a cushion for bulky seams.
The extra layer of supporting fabric between the outside fabric and bulky seams keeps bulk from being obvious and from pressing through to form an unattractive ridge or welt; the bulky pleat of a bound buttonhole is a prime example.
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