I saw this weird type of wirenut at Lowe's last week.
The underside opening where the wires are inserted was covered by little plastic teeth "flaps". According to the package, the inside of the wirenut is packed with an anti-corrosion compound.
The package also states that you cannot reuse the wirenut (as if I were to do that anyway).
Don't remember the brand right now. Is anyone else familiar with what I'm talking about?