|Update 4/22/05 I have figured out a variation on this that even works for bulkier/stiffer fabrics...
Updated Slightly Stretchy Waistband
I first encountered this technique in a Threads (# 54) article on Donna Karan's wardrobe elements. Sandra Betzina has included it in her books, calling it the 'Designer Waistband that Grows'. It is a great technique and makes for very comfortable waistbands. The general idea is that the interfacing in a waistband is replaced by elastic. In a nutshell, the steps are
1) Before you cut, adjust the pattern (use your favorite method) to increase the garment waistline (and the waistband) so that it measures 2 - 3 inches MORE than your HONEST waistline measurement.
2) Sew the waistband to the garment with a 5/8" (preferably - it's easier to anchor the elastic to a wider SA) seam allowance; finish the other long edge.
3) Cut a piece of elastic the width of your desired finished waistband so that it is about 2 - 4 inches LESS than your waistline measurement (the actual measurement depends on the stretchiness of the elastic)
4) Quarter mark the waistline seam allowance and the elastic
5) Place the elastic so that it is between the seam allowance and the waistband, with one edge on the waistline seam
6) Turn the waistband toward the garment so that the seam allowance extends and overlaps the elastic, then machine baste across the elastic and the seam allowance ONLY at each end and at each quarter mark. This stitching is perpendicular to the waistband.
7) With the seam allowance extended and next to the feed dogs, and the elastic facing up, zigzag the elastic to the seam allowance, stretching the elastic to fit the waistband as you sew. Remove the basting.
8) Fold the ends of the waistband in half, RS together, with the finished edge folded to the wrong side so that the folded edge matches with the waistline seam; stitch across the ends, trim the seam allowances and turn the ends right side out, over the elastic.
9) Fold the waistband over the elastic, wrapping it tightly to the wrong side and pin the finished edge to the garment.
10) Vertically machine baste at regular intervals through the waistband and the elastic (I've tried skipping this step - it's not worth it! )
11) From the right side, stitch the waistband in the well of the seam; remove basting
12) Hand sew a trouser hook-and-eye to the ends of the waistband
13) Enjoy your nice, comfy, stretchy waistband the next time you go to a potluck supper…
For a more detailed description, including pictures of the process, see Power Sewing Step-By-Step by Sandra Betzina, pages 115-118