How to Sew Bra Cups into a Swimsuit or Top

By Prymamericas.com: Sewing, quilting, and knitting supplies | Published: 2026-10-23

Category: How-to Guides

Learn how to sew molded foam bra cups into a swimsuit or top for shape and support. Step-by-step guide with tips for a smooth, professional finish.

Quick answer

Sew molded foam bra cups into your swimsuit or top by positioning them inside a lining or built-in shelf, pinning in place, and stitching along the edges with a zigzag or stretch stitch.

Choosing the right bra cup for your project

Molded foam bra cups work well for swimwear and formal tops because they hold their shape when wet and provide consistent support. The Dritz Molded Foam Bra Cups come in a polyfoam/tricot knit cover that is machine-washable and dry-cleanable, making them a practical choice for garments that need frequent cleaning.

When selecting a size, hold the cup against your bust to check coverage. The cup should sit smoothly without gaping or pressing too flat. If you are between sizes, try the larger option for a more comfortable fit under a lined garment.

Step-by-step: Sewing bra cups into a swimsuit or top

1. Prepare the garment and cups: Turn the top inside out. If it has a separate lining or built-in shelf bra, that is where the cups will go. If not, you can add a lining layer. Place the bra cup inside the lining so the curved side faces outward toward the body. Make sure the cup sits flat and the center edge aligns with the garment’s center front.
2. Pin the cup in place: Use small, sharp pins to secure the cup to the lining along the top, bottom, and side edges. Keep the pins parallel to the seam line so you can stitch over them or remove them easily. Pinning at the edges prevents the cup from shifting while you sew.
3. Stitch the cup to the lining: Using a zigzag or stretch stitch, sew along the outer edge of the cup, about 1/8 inch from the foam. Stretch the fabric slightly as you sew to match the cup’s curve. Avoid stitching through the outer layer of the garment. A straight stitch may pop when the fabric stretches; use a stretch stitch for swimwear.
4. Check the fit and trim excess: Try the garment on right side out. The cup should stay in place without wrinkling the outer fabric. If the lining puckers, trim any excess fabric around the cup, leaving a 1/4-inch seam allowance. Test the fit before trimming; once cut, you cannot add fabric back.
5. Finish the edges (optional): For extra durability, sew a second line of stitching 1/4 inch from the first, or use a narrow zigzag to encase the raw edge of the lining. This step is especially helpful for swimsuits that will see heavy use. Double stitching prevents the cup from shifting after many washes.

Product facts

Molded Foam Bra Cups, White: Firm molded foam cups with a polyfoam/tricot knit cover; machine washable and dry cleanable. The firm shape holds up in swimwear and formalwear, and the washable cover makes care easy after repeated use.
Molded Foam Bra Cups, White