All About Polyester (Microfiber, Microfleece, Microsuede) Cloth diapers can be made of many materials, but polyester is the main material in the most popular diapers and covers.

First, some terminology for all fabrics:

Fibers are the individual tiny bits of material that are spun into threads.  For diapers, thread can be made of polyester, cotton, hemp, bamboo or wool.  (Material refers to the source.)

Threads are knit or woven into fabric.  Some common fabric types are terry (knit with loops, like a bath towel), gauze or twill (woven with a diagonal pattern like in prefolds or khaki pants), fleece (brushed on the inside to be fluffy) and interlock (knit like a dense sweater.)

Now, we can combine these two things and get many combinations: cotton terry as a bathtowel, wool interlock as a diaper cover, hemp knit as a doubler, etc.  This is where the confusion starts.

First, let's look at polyester.  Polyester is a man-made material used in many products that we use everyday.  It is the material in all covers, pocket diapers, and most pocket diaper inserts.

The type of polyester in diaper covers and pocket diaper outside is called PUL (polyester-urethane laminate.)  It is waterproof.  It is stretchy because it is a knit.

The polyester used inside pocket diapers as the stay-dry material is either microfleece (FuzziBunz), microsuede (bumGenius) or microchamois (Rump-a-Rooz.)  It is not waterproof, but neither does it absorb water.  It acually wicks moisture along its fibers, so the urine wicks along the fibers to the other side.  This allows the baby to feel dry even if he has peed.

The polyester used in most pocket diaper inserts is called microfiber.  It is a terry fabric and when it is new, it "grabs" the dry skin on your hands.  The way it works is that it has many tiny threads that increase the surface area.  More surface area = more area for absorption.  This is what makes it excellent for a pocket diaper insert - it can absorb a lot, and quickly.  This also makes it important to never put the inserts next to the baby's skin, as it can dry out the skin.

The interesting properties of microfiber inserts have some other effects - they can retain odors (commonly referred to as "microfiber stink.")  Luckily, polyester's durability means that you can easily remove the stink by washing the inserts with 1-2 Tablespoons chlorine bleach (make sure there is nothing but the inserts in this load.)

The tiny fibers can also trap excess detergent, which can contribute to odor.  Using bleach will help break this up, but it is important to not use too much detergent.  Most people use too much.  I wash about 40 diapers at a time in a front-loader and only use 1 Tablespoon detergent.

Overall, once you understand how polyester works and how to care for it, you can see why it makes great inserts for pocket diapers.  Some people, however, will not want to use polyester as it is a man-made fiber.  In this case, you will need to use cotton, hemp or bamboo diapers with wool covers.