This cover will fit from about 6-35+ pounds. It is a very generous cover. (I know I say that a LOT in the review, sorry!) You can get it in either snaps or hook and loop closure. The insides are made of biodegradable TPU waterproof material. Biodegradable TPU is solvent-free. Biodegradable TPU is a polyester fabric that has been laminated with a thermoplastic polyurethane using a heat bonding process. This process is low in toxicity and is better for the natural environment. Both the TPU laminate and the polyester fabric the laminate is applied to are biodegradable. When composted they will biodegrade in 4-5 years. It is more breathable and "earth friendly" than the usual PUL.
I have yet to test it with a poopy diaper but I'm sure it would hold everything in very well! It is so strechy! I thought it would leave red prints on my son if I snapped it down too small but it didn't (and he took a long nap in it). He is 1 year old and he is pretty skinny (about 20 pounds or so). He is on the second snap setting and I LOVE the fit on him. I put a fluffier diaper on him today and it still fit wonderfully! I am excited to keep using this diaper cover. He still has room to grow in it too which I love.
I would give this diaper 5 stars. So far there has been no problems and I am loving it!
*EDITED TO ADD* I have used this over night and with poo dypes and it still is working great. I still give this a 5 star review, months after I have bought it.