We got these trainers from Bummis, and purchased them locally at No Pins Required, our favorite (and really, our only, local brick and mortar diaper shop). I purchased a "size medium" in the classic Bummis jungle print - we've had 2 covers in 2 different sizes in the same print. A variety of sizes are available; I've only found these in white and the jungle print.
Materials: The outside is the typical Bummis knit. There's a hidden layer of PUL throughout the trainer. There's a flannel liner inside to help kids feel that they're wet. There are also 3 layers of terry in through the wet zone, which should be enough to contain a fairly substantial amount of urine.
Closures: I wish they had snaps - the longer we do this, the bigger deal the snaps become. The elastic is stretchy, but makes the rest of the trainer look a little poofy.
Sizing: Acorn is about 29 lbs, and mostly wears size 2T clothes - he can wear most 18 month pants, but they're too short, and he can wear 3Ts but they're too long.
We purchased a medium. They *look* huge. The sizing chart says SMALL: 9-14 kg (20-30 lbs), MEDIUM: 14-18 kg (30-40 lbs), LARGE: 18+ kg (40+ lbs). I looked at the size small, but in comparison to the medium, they are not really much smaller at all, and I wanted these to last for a bit. The poofy look kind of goes with the way they fit too - they seem poofy around the bottom, and I'm not really sure these would work well under clothes.
Absorbency: These were among the fastest to wick up the front and back of the wet zone, all the way up to the waist band. There was a bit of puddling at the leg openings, but it didn't run out the legs; it soaked in. That said, these trainers definitely won't hold more than 2 oz.
Drying: These are consistently one of the first dry, and I've never had a problem with them coming out of the dryer wet.
Final thoughts: These are ok. I think the lack of snaps makes this somewhat disappointing for us.
Disclaimer: these trainers were bought by me, and this review is my personal opinion of them. No compensation was provided.