What's the deal with diaper covers?

Rather than re-writing a whole new article when someone else has already done it so wonderfully, I'll just link you to her blog post.

All About Diaper Covers from The Mommy Goods

There are just a couple things I'd add:

One, there's another type of material that works identically to PUL, only it's called TPU.  Many diaper makers, such as Rumparooz, are starting to use TPU over PUL.  While PUL works great, it's not so great for the environment.  PUL is poly-urethane laminate polyester fabric that is created using a chemical process. TPU is a similar waterproof material that is solvent-free - it's the same polyester fabric, but instead of using a poly-urethane laminate that is done with chemicals, it's a thermoplastic polyurethane that is created with a heat bonding process.  It's lower in toxicity and better for the environment.  TPU is also biodegradable and will biodegrade in 4-5 years if composted. Since many people who cloth diaper have great concerns about the environment, this is something to keep in mind. (Wool would obviously be another environmentally friendly choice). Personally, I think that TPU is a tiny bit softer as well, but that could be my imagination.

Also, keep in mind that most types of wool often can stretch quite a bit to fit your child for a while; however, it is still a sized cover, and the same soaker won't take your child from birth to potty training. On the flip side, PUL and TPU covers can generally be purchased in either sized or one-size versions.

Both PUL and TPU can delaminate, which means that the waterproof part separates from the fabric part.  If this happens, you can try to return the diaper to the manufacturer for a replacement.  You can still use a delaminated diaper - be sure to line dry only! - but if the laminate part rips, the diaper will leak through the tear.  Line-drying PUL and TPU covers will help them last longer; however, both should be dried on high the first time you wash them to help seal the laminate (unfortunately doing that won't fix a delaminated cover).

Finally, if you put PUL or TPU covers (or diapers) in the dryer, do so on low heat (after the first initial high heat dry).  Try not to stretch the elastic in the diaper until it has completely cooled from drying to lengthen the life of the cover.

Wild Coconut Wear wool cover (soaker)

Thirsties PUL cover

 Thirsties PUL cover (open)

Wild Coconut Wear wool longies

WAHM wool soaker

Woolly Bottoms wool footies

Kissaluvs wool soaker

WAHM fleece soaker

Flip PUL cover (technically part of an AI2 system, but can be used as a regular cover)