A braided elastic narrows when stretched and can lose stretch and recovery if it is pierced when stitched. Knitted and woven elastics retain their original width when stretched. There are special elastics for cycling pants, swimwear, lingerie and sweatpants. Select a seam with enough stretch for the fabric. Use a plain seam for stable and moderate-stretch knits.
Serger seams to neatly trim and finish the edges.
Seam allowances stitches best used with knits. Since knit fabrics don't ravel, seam finishes are generally not necessary. If the cut edges ravel or curl, use a narrow zigzag stitch to add stability. Reinforce knit seams with woven tape. Seams that get a lot of stress and may stretch out of shape, such as shoulder, neckline, and waistline seams, need to be taped for stability.