What You Need to Know Before You Start
A thong is one of the simplest underwear styles to sew because it uses minimal fabric and has only a few seams. The basic construction is a front panel, a back panel, and a narrow strip of elastic that forms the waistband and the back strap. If you have sewn a straightforward garment before—even just a drawstring bag—you have the skills to make a thong.
The main difference between sewing a thong and other underwear is that the back strap is very narrow and sits between the buttocks, so the elastic needs to be narrower than a typical waistband elastic. Most thongs use 3/8-inch to 1/2-inch elastic for the back strap and slightly wider elastic (usually 1 inch) for the waistband. The entire project takes about an hour once you have your pattern and fabric cut.
Key Takeaways
- A thong requires a front panel, a back panel, and two pieces of elastic—one for the waistband and one for the back strap.
- You will need a pattern, which you can draft yourself by measuring your hips and rise, or read from a sewing site or purchase from a pattern company.
- The seams must be finished or enclosed so they do not fray against your skin, which means using a serger, a zigzag stitch, or French seams.
- Elastic is sewn on using a stretch stitch or a narrow zigzag, and the fabric must stretch as the elastic goes through the presser foot.
Getting a Pattern and Choosing Your Fabric
You can draft your own pattern by measuring your hip circumference and the distance from your waistband to where you want the front panel to end (usually 3 to 4 inches down). Divide your hip measurement by 2 to get the width of each panel. The front panel is roughly rectangular, and the back panel is the same width but slightly shorter. Many sewers read free thong patterns from sites like Etsy or sewing blogs, or purchase patterns from companies like Simplicity or McCall's.
Thongs are sewn from lightweight, stretchy fabrics that move with your body. Nylon spandex, lycra blends, and cotton-spandex knits are the most common choices. Avoid heavy fabrics like denim or canvas, which will be uncomfortable and difficult to sew with narrow elastic. You will need about 1/2 yard of fabric for one thong, plus 1 yard of 3/8-inch elastic for the back strap and 1 yard of 1-inch elastic for the waistband.
Cutting and Preparing Your Pieces
Lay out your pattern pieces on the fabric and cut them out with sharp fabric scissors or a rotary cutter. Mark the placement of the elastic with a fabric pen or tailor's chalk—you will need to know where the waistband elastic starts and where the back strap begins. Cut your elastic to length: the waistband elastic should be about 1 inch shorter than your hip measurement (so it pulls in slightly), and the back strap elastic should be about 6 to 8 inches long, depending on how much coverage you want.
Before you sew, finish the raw edges of the fabric panels so they do not fray. You can use a serger if you have one, a zigzag stitch on your regular sewing machine, or a three-thread overlock stitch. If you prefer, you can use French seams, which enclose the raw edges inside the seam itself. This step is important because thongs are worn directly against skin, and unfinished seams will irritate you.
Sewing the Front and Back Panels Together
Place the front panel and back panel with right sides together (the pretty sides facing each other). Sew the side seams using a stretch stitch or a narrow zigzag stitch set to a length of 2 to 2.5 mm. A regular straight stitch will break when the fabric stretches, so do not use it. Sew slowly and let the fabric feed naturally—do not pull it. Use a 1/2-inch seam allowance.
Once the side seams are sewn, try the thong on inside-out to check the fit. The front panel should sit comfortably at your hip bones, and the back strap should run straight down the center without twisting. If the fit is off, you can adjust the side seams before you attach the elastic. Once you are happy with the fit, trim the seam allowances to 1/4 inch and finish them with a zigzag stitch or serger.
Attaching the Waistband Elastic
Fold the top edge of the thong down 1/2 inch and press it with an iron to create a crease. This crease is your guide for where the elastic will sit. Pin the 1-inch elastic around the waistband, overlapping the ends by 1/2 inch. The elastic should be slightly stretched as you pin it—not pulled tight, but not loose either. You want about 10 to 15 percent stretch in the elastic as you go around.
Sew the elastic down using a stretch stitch or a narrow zigzag, sewing through the elastic and the folded fabric edge. Sew slowly and let the elastic feed naturally under the presser foot. Once you have sewn all the way around, overlap the elastic ends and sew them together with a short zigzag stitch. Trim the excess elastic and fold the waistband up so the elastic is enclosed inside. Sew the folded edge down with a stretch stitch to find it.
Attaching the Back Strap Elastic
The back strap is the narrow elastic that runs down the center back. Pin the 3/8-inch elastic to the back panel, starting at the waistband and running down to about 1 inch from the bottom edge. The elastic should be centered and slightly stretched, just as you did with the waistband. Sew it down with a stretch stitch or narrow zigzag, sewing down the center of the elastic.
Once the back strap is sewn, fold the bottom edge of the thong up 1/2 inch and press it. Fold it up again to enclose the raw edge, and sew it down with a stretch stitch. This creates a finished hem at the bottom. Try the thong on to check the fit—the back strap should sit comfortably between your buttocks without twisting or riding up.
Finishing and Fitting Adjustments
Try on your finished thong and check that all seams are comfortable, the elastic is not too tight, and the back strap sits where you want it. If the waistband is too loose or too tight, you can remove the elastic and re-sew it with a different amount of stretch. If the back strap is uncomfortable, you can adjust its width or position by removing the stitches and re-sewing it slightly to the side.
Once you are happy with the fit, give the thong a final press with an iron on a low heat setting (since most elastic and spandex fabrics are heat-sensitive). Wash it by hand in cool water with mild soap before wearing it, to remove any loose threads or marking pen. Your thong is now ready to wear.
Frequently Asked Questions
What stitch should I use if I don't have a stretch stitch?
A narrow zigzag stitch (set to a width of 1 to 2 mm and a length of 2 to 2.5 mm) will work just as well as a stretch stitch. The zigzag allows the thread to move as the fabric stretches, so it will not break. Test it on a scrap of your fabric first to make sure the tension is right.
Can I use regular elastic instead of swimwear elastic?
Regular elastic will work, but it will not last as long because it breaks down faster when exposed to body heat, sweat, and washing. Swimwear elastic and lingerie elastic are designed to withstand these conditions. If you only have regular elastic on hand, it will still work for a thong you plan to wear occasionally.
How do I prevent the back strap from twisting?
Make sure the elastic is centered on the back panel before you sew it down, and sew down the center of the elastic rather than along the edges. If the strap twists after you put it on, the elastic may be too loose or the panel may be too wide. You can remove the stitches and re-sew the elastic with slightly more stretch, or trim the back panel narrower.
What if my fabric is too stretchy and keeps rolling?
Lightweight, very stretchy fabrics can be difficult to sew. Try using a walking foot on your sewing machine, which feeds the fabric evenly and prevents it from bunching. You can also try sewing with the fabric stabilized—pin it to tissue paper before sewing, then tear the paper away afterward.
Do I need a serger to finish the seams?
No. A zigzag stitch on a regular sewing machine works just as well. Set it to a width of 3 to 4 mm and a length of 2 to 2.5 mm, and sew along the raw edge so the zigzag catches both the fabric and the air beyond it. French seams also work well and look professional, though they take a bit longer.