|This is great for when you're using a heavy fabric and don't want the added bulk of a facing, are too short on fabric to cut facings, want a thin yet sturdy waist, for short waisted people or those who have shirts that come untucked. Grosgrain ribbons were big in haute couture in the '50s--there's no reason why not to bring 'em back!
Use a wide 38mm/1.5" grosgrain ribbon. Measure your waistband by laying it out flat (on your ironing board) and measure with a measuring tape on its side so it can curve along the waist. Double this measurement to get the whole waist. Add 2.5cm/1" to accomodate folding over at the ends (by zipper) and cut. Shape the ribbon into a curve, pressing with plenty of steam. (Poly ribbons take low/med heat and don't press as well as acrylic.) Let cool. Pin the "tighter" surved side on RS of fabric Fold over the ends and place folds up directly over the zipper tape. The folds will face inside after the facing is in. Place at any seam if you're not using a zipper. Stitch, then fold back over. Press over a tailor's ham if you have it--I don't, and mine are fine. Stitch the facing in the ditch of seams and darts (while you're at it, might as well do a good job) so your facing will never flop out or roll.
Grosgrain ribbons are often seen in little girls' hair. They are horizontally ribbed. I don't recommend satiny ribbons, because the smooth surface will make the waist move when you do, and you can forget tucking in a shirt. They probably don't shape as well either with steam, but I haven't tried. Acrylic ribbons are the best, as they take a press and will gradually stretch to your shape; but I can only find polyestor. Poly works fine. Some smaller width grosgrain ribbons have a anti-fray ridge running along the edges of the ribbon. This would make it difficult to shape with steam. Look for ribbons with ribs going completely across.