The following is an opinion piece on fabrics in diapers. I feel an opinion piece is valid as I have been sewing since I was 3 and am now 39. Also I am currently cloth diapering my 6th child over the past 18 years. Understanding fabric choices is important. One thing all good seamstresses know is that the best seamstress with the best pattern won't make a good item without the right choice of materials.
CLASSIC COTTON FOR DIAPERS: diapers used to be all cotton, usually flannel or Birdseye. There is even diaper flannel. Cotton is a natural fabric and washes and dries well. I rate it 10/10 on a scale of 1(poor) to 10 (excellent) on how well it washes. If stained it suns well (hanging in the sun to get out stains) . It is absorbent and has stood the test of time when it comes to diapers. This is a healthy, clean and reliable choice for cloth diapers. You can use other cottons too such as t-shirts (not very absorbent) or old sweatshirts. You can also use cotton batting in the core of a diaper so long as you quilt it. You can use FST'S (flour sack towels) and cotton Terry (old towels), both are very absorbent. Softer French Terry (still absorbent because the shape of the fibers draws wetness in and distributes it). Burly Knit Terry (bkt) is a Terry with extra long thick loops. Its super absorbent but very thick so best used as an insert rather then through a whole diaper.
HEMP: Everything I've said for cotton goes for hemp; just double the absorbent factor, unfortunately the cost is also higher. Its a wonderful addition to the natural fabric options for diapers. For wash rating I give it 10/10
BAMBOO (rayon): If you can find it in hemp you can find it in bamboo rayon. Like Hemp it is very absorbent. The difference is bamboo is chemically processed into rayon and is not a natural fabric. If you see it listed as such (except for bamboo linens which aren't used in diapers) you should report it. Zorb I & II are also bamboo rayon . Zorb is very absorbent! However it doesn't always hold everything it absorbs. Its texture and construction are much like batting, but thicker. Charcoal Bamboo is popular but it is exactly what it says, bamboo (rayon) with actual charcoal in it. It washes great for a synthetic and I'll give it 8/10. If you want to read more about the truth behind bamboo check out this news article here. You can also read my post titled "the heartbreaking truth about bamboo".
MICROFIBER: Its generally used to make inserts to stuff pocket diapers. It cannot be used against babies skin as it will suck the moisture out of your babies skin. As an insert it will be effective in the diaper. What you should know is that microfiber was created by the cleaning industry to trap dirt and germs. It does this effectively. The downside is it's very effective which makes it difficult to clean. It is more prone to ammonia issues then any other fabric choice. The trapping germs part (personally) worries me about its use in diapers. I'll rate it 1/10 on its ability to wash clean
FLEECE: There are a variety of fleeces and they do not all do the same thing. Some wick, absorb and some are water resistant. Fleece is polyester (chemically made). It can be made with bamboo but it is not organic despite the title organic bamboo fleece (OBF), this is because bamboo is creatrd through a cellulose process. Cotton or hemp fleece that isn't poly blend is for absorbtion. Polar fleece and Windpro (which is a polar fleece) are water resistent. They are used on the outside of diapers or as diaper covers. They can suffer compression leaks. They are soft and let air circulate.
Microfleece is a moisture wicking fleece. It is used on the inside of a diaper to create a soft feel dry layer. Fleece washes well enough. They rank in the middle wash wise in that they won't wash as well as cotton but better then mocrofiber. I'll rate it 7/10 on washing clean.
VELOUR AND SUEDE CLOTH: Velour is uses on the inside of a diaper for a feel dry layer. The kind used for diapers is polyester backed. Without the poly backing it will wear out quickly. Velour is cotton, organic cotton and bamboo cotton. OBV stands for organic bamboo Velour but is not organic. Suedecloth works and is used like the velour. It resists staining. But its not as soft. They does not wash well and is prone to ammonia. I'll rate it 3/10 for ability to wash clean.
MINKY: This is also polyester. t is super soft and moderately absorbent. It might be used on the inside or outside of a cloth diaper. It's popularity is based on its amazing feel and look. wash wise I rank it 5/10.
PUL: This is Polyurethane. It is used as a diaper cover, outside of AIO's or inside as a hidden waterproof layer and same on pocket diapers. It is waterproof. It needs a different wash routine as a cover then a regular diaper. However since it might be sewn as part if the diaper the whole diaper then requires a different wash routine. A cheap PUL will delaminate. Over time PUL will wear out especially when not used as a seperate cover. It can make the inside of a diaper humid against babies skin. It does wash clean though. Wash wise (clean speaking) I give it a 9/10.
TAFFETA: I have never sewn a taffeta cover but I have used one by Kushies. Its waterproof but unlike PUL it breathes. It is also thinner then PUL and longer lasting. It has no stretch to it though so it's not good as an os (one size fits all). Im not sire why its not more popular and not available as a diaper fabric. It is a synthetic fabric but also washes well and I give it a 9/10.
WOOL: This is the hero of the diaper cover world. It is used as a seperate cover. It sounds complicated to wash but it isn't (check out my posts on wool). It Breathes, its natural, its water repellent, it's natures raincoat. I have no leaks with wool at all, not even overnight. If your having leak issues this is my recommendation hands down. It is pricey but you can use upcycled wool which is cheap. Wash wise I rank it 10/10.