Definition
Underlining is a layer of fabric cut like each garment piece and basted to its wrong side before construction, so the two layers are sewn as one.
Underlining changes the fabric itself rather than adding a separate layer inside. Each garment piece is cut twice, once in the fashion fabric and once in the underlining, and the two are basted together around the edges within the seam allowance. From then on, you sew them as a single layer.
What it is for:
- Opacity: a white linen or a pale silk stops being see-through.
- Body: a soft fabric gains enough structure for a fitted dress or skirt.
- Stability: loosely woven fabrics, such as some bouclé or linen, keep their shape and fray less.
- Hidden stitches: hems, facings and darts can be hand-stitched to the underlining, so nothing shows on the outside.
- Marking: pattern markings go on the underlining, never on the fashion fabric.
Choose an underlining that is light and stable and shares the care needs of the main fabric: silk organza for body without weight, cotton batiste or voile for opacity and comfort, muslin fabric for firmer structure. Prewash both fabrics if the garment will be washed.
Smooth the fashion fabric over the underlining on a table, matching the grainlines, and baste with long stitches about 1 cm (3/8 in) from the edge. Baste darts through both layers along their center before sewing them.
Underlining is different from lining, a separate inner garment, and from interfacing, which stiffens only selected areas.