Several factors determine which shapes, sizes and materials will work best for you.

What is your flow like - watery, thick, unpredictable? If your flow is very watery, you may want your pads to have a water resistant layer such as synthetic fleece or PUL. If your flow tends to sit on top of the pad rather than absorb quickly, you'll want a textured material on top such as flannel, velour or terry.

How heavy is your flow? Generally, the heavier your flow is, the more pieces you'll need at a time, and the more frequently you'll need to change.

How much time do you prefer between changes? If you don't anticipate being able to get into a restroom for several hours, layering up is a good idea. A water resistant layer can also help to distribute flow within the pad and keep it from leaking through.

How concerned are you about a trim fit? Some women like the security of a soft, fluffy pad, and some prefer not to be able to feel that the pad is there at all.

Cotton terry and hemp terry absorb about the same amount of liquid, but cotton terry is fluffier so it has more surface area to catch and absorb liquids before they run off the top or pass straight through.

Synthetic materials help to cut down on bulk, but can make the pads warmer and less breathable.

The Fabric Comparison Guide gives more info about the materials available at Amy's Rag Bag.

What's your underwear like? Cloth pads don't have the adhesive strip that disposables have, so your underwear has an important part to play in keeping your pads in place. Wear slippery, thin materials and baggy underwear at your own risk. If you do wear them, you'll need bigger pads with flared ends to compensate for any shifting.

The best underwear are made of mostly or all-natural materials and have a snug fit with a little bit of stretch. Briefs and boy-cut underwear usually give the best support, while high-cut bikinis sometimes don't have enough contour and old-fashioned hipsters can be too narrow in the crotch.

What's your size? Contrary to popular belief, taller and larger people do not usually need wider pads than the more petite. Standard crotch width for almost any size underwear is 2 3/4 inches, but there is variation in styles. Size does make a difference in the length of the pad - particularly in the crotch length, which is the narrowest part. The pieces on the right are cut with longer crotches.