Zpacks used to “hide” this option…but now they are fully offering it on their accessories page. ->
http://www.zpacks.com/accessories/double_wall_insert.shtml
Basically, very similar to the tarptent double rainbow insert. Joe used to hide it b/c in most conditions this isn’t needed, and he didn’t want to give customers the wrong impression that it “is” needed, though it does talk about that in depth on the page.
But at least I feel we can talk about it openly now.

