From the Manufacturer

We fear that if we don't load these exquisite inserts onto our site soon, it will be just another night you will regret not having so many layers of charcoal meets PUL for an overnight sleeping experience hither-to unknown.

As you can see, we've taken the best of both worlds: charcoal cloth, for extra absorbency for those of you particularly blessed with heavy wetters (or babies who sleep through... we have heard of such babies but have yet to personally know one... sigh), plus a layer of waterproof PUL which rests against the gusset of the diaper cover, giving you a lil more peace-of-mind when you check in on your sleeping angel first thing in the morning.