According to the Textile Glossary, a shelf bra is "a bra that is built right into the garment." What does this mean for you? Comfort, as well as less clothing—something which is especially welcome when the weather grows warm. Thanks to the shelf bra, you won't have to wear a bra and a shirt, top or dress, rather the garment with the bra built in. Best yet, you can alter existing garments by sewing a shelf bra into them.
Cut open a paper bag so it becomes one large piece of paper.
Turn your tank top or garment inside out.
Trace the shape of the neckline onto the paper.
Measure the width of the tank top and write that measurement down. If the tank top is tailored, trace that shape onto the brown paper.
Draw the pattern for the shelf bra on the brown paper. It will follow neckline of the tank top, have the tank top's width and be 6 inches from the neckline to the bottom of the shelf bra.
Cut the T-shirt along the side seams so it's in two sections.
Pin the pattern for the shelf bra to one of the T-shirt sections.
Trace around the pattern with tailor's chalk. Trace around the pattern again but add 1/2-inch for seam allowance. On the bottom of the shelf bra, add a 1-inch seam allowance.
Cut out the shelf bra.
Press up the bottom of the shelf bra along the line for the seam allowance. Turn under the raw edge of the fabric and sew along the folded edge, making a channel for the elastic.
Lay the tank top on your work table. Pin the shelf bra piece to the neck of the tank top, right side of the shelf bra to the tank top. The bottom of the shelf bra should extend up beyond the top of the tank top. Hand sew or machine sew the shelf bra to the neckline of the tank top.
Press down the shelf bra so that the bottom of the shelf bra is now lying on top of the inside front of the tank top.
Measure around your ribcage just below your breasts. Divide that number in half. Cut the elastic to this length.
Pin the sides of the shelf bra to the side seams of the tank top. Make sure the shelf bra lies flat and evenly on the tank top. Sew the shelf bra to the tank top along the seams of the tank top. Do not sew through the channel for the elastic.
Thread the elastic through the channel. Pin the elastic on both ends so that it does not disappear into the channel. Sew through the seam, closing the channels securing the elastic in place. Turn the tank top right side out and put it on. Enjoy your new sewn-in shelf bra.