You need two pieces of decorative cotton fabric, a similarly sized piece of cotton batting and cotton thread in a complementary color to make a potato baker bag. The size and style of the fabric depends upon the size of your microwave, your needs and personal preferences. Use 20-inch by 11-inch pieces of fabric to create a bag that holds two large potatoes, or start with 22- by 13-inch pieces to bake four medium potatoes.
Potato baker bags are intended for use in the microwave, so the bags must be constructed from threads and fabrics made entirely from cotton. One piece of fabric serves as the liner of the bag, and the other piece is the outside cover. Use the same design for both pieces for a simple appearance, or choose two different styles to create a unique look.
Lay the cover fabric face down on a smooth surface, cover with the batting, and place the remaining fabric face-up on top. Quilt the layers together in 6-inch blocks, and then sew all four edges. Hem the wide edges using a 1/2-inch seam. Fold the potato bag into an inside-out square, overlapping the edges by about an inch. Sew all of the edges using a 1/2-inch seam.
Machine wash and dry the potato bag inside-out before using. Reverse the material, place washed potatoes inside the bag, and microwave according to your oven size and the number of potatoes. Do not pierce potatoes before microwaving them in a baker bag.