When it comes to absorbency, fitted nappies are unbeatable! Especially for nights, naps or long trips, fitted nappies are simply optimal.
Fitted nappies are made of 100% absorbent material, so they can stay tight for up to 12 hours. Nevertheless, they do not have a waterproof outer layer, so they should be worn with waterproof overpants, e.g. PUL covers, wool covers or pull-up covers.
Here you can learn in detail how fitted nappies work.