They're basically a nice piece of fabric sewn up in a way that's supposed to help absorb wetness as part of a diapering system. (amazon.ca)
The diaper's revolutionary soft dry touch liner absorbs wetness in seconds, ensuring your baby is dry and comfortable. (kaboutjie.com)
The fleece lining not only works to help keep your child comfortable and soft, but also is fitted with charcoal and bamboo to help absorb wetness. (earlymomentsmatter.org)