Uses: Hems are used on the bottoms of tops, dresses and sleeves. Because the best-looking hems are topstitched, it is important to have very straight hems to catch the fabric underneath.
Materials: Thin cardboard (think cereal boxes) or manila envelopes. Cut in to strips: the first should be the width of your desired hem, the second should be 1/8" shorter. I cut mine at 11/2" and 1 1/8"
For more on hems, check out Sew,Mama,Sew!'s lengthy guide to choosing the right hem width for your garment.
Check out the tutorial on Burda Style.