These mattresses will not only stay dry no matter how big a leak is, it actually works to keep your baby safe from other harmful dangers as well. (earlymomentsmatter.org)
Their overnight pads are helpful for overnight and the times of big leaks like the first few weeks. (lactationlink.com)
You don't need a very big leak to let enough air into the system to be a problem as the issue is not so much fluid getting out as air getting in. (mechanics.stackexchange.com)