You can purchase lace in widths as narrow as ½ inch and as wide as six or eight inches. Choose cotton, polyester or a fiber blend. Or use antique lace or handmade lace. This is a good way to salvage a damaged lace tablecloth or shawl. If you intend to launder your throw pillow, use a washable lace, which will stand up better to wear and tear. Wide lace can stand alone as a ruffle. If you decide to use narrow lace, sew several rows of lace to fabric.
Make your ruffle by making a simple running stitch along one edge of the lace, then drawing the thread up to gather the lace into a ruffle. Or sew your lace to a piece of fabric that matches the pillow back or front, and gather this fabric into a ruffle. The fabric shows through the lace, emphasizing the pattern of the lace.
Pin your ruffle to the right side of the front of your pillow, matching the inside edge of the ruffle to the edge of the pillow top. The outside edge of your ruffle faces the center of the pillow top. When you cover the pillow top and lace with the pillow backing and sew a seam almost all the way around, then turn the pillow right side out, your lace ruffle will face out, away from the pillow. Stuff the pillow and sew the opening closed.
If your lace is limp, use heavy starch to perk it up. Instead of gathering your own lace into a ruffle, you can also purchase pre-gathered lace and attach it to your pillow. If you wash your pillow cover, you may need to touch up the lace with a moderately hot iron. You can also add a double layer of ruffles, with a narrower ruffle on top of a wider one, for a more luxurious look.