A cotton slip is cool on a hot day, especially if it is full enough to keep your skirt away from your legs. A full slip also improves the lines of a gathered skirt. Ready-made cotton slips are sometimes hard to find, but you can sew one yourself with only a few straight seams. Make an inexpensive slip from muslin with eyelet trim or use fine batiste and handmade lace to make an heirloom petticoat.
Measure your waist.
Cut your fabric two or three times as long as your waist measurement. This will be the measurement around the hem of the slip: two times the waist measurement for a slightly full slip, three times the measurement for a moderately full slip. If you need more fullness wear two slips; adding more fabric to a single slip will make the waist too bulky.
Cut your fabric to the desired length of your slip.
Sew the sides of the fabric rectangle together to make a large fabric tube. Use a 1/2-inch seam allowance. Finish the seam allowance with a zigzag or overcast stitch.
Finish the lower edge of the slip with a zigzag or overcast stitch, then sew the trim around the bottom of the skirt, starting at the seam. Fold under the raw edge of the last 1/2 inch, then lap it over the beginning of the trim and sew closed to give it a finished look.
Finish the top edge of the slip with a zigzag or overcast stitch.
Iron down a 1-inch casing for the elastic at the top of the slip. Sew 1/4 inch from the edge of the folded down fabric, leaving a 2-inch opening at the end for threading the elastic.
Cut a length of 1/2-inch-wide elastic that will fit comfortably around your waist with a 1/2-inch overlap at the end.
Thread the elastic through the casing with a safety pin or elastic threader. Be careful not to twist the elastic.
Sew the ends of the elastic together with a 1/2-inch overlap. Sew the opening in the casing closed.