Yes CubanFibre is nominally waterproof but if something inadvertantly comes to be touching the sides, like say you have all your gear in there on a rainy night and while you're sleeping some of it gets pushed around, you will wake up in the morning w wet stuff. Ask me how I know this.
Or, you can take ZPacks word for it (from their web site) "All single wall shelters will get some condensation in cold humid conditions."
And I wasn't refering to frozen ground for staking sometimes being a problem. Their tents are pretty sensitive to being precisely staked in order to get a tight pitch and there has been a couple of times 4 stakes are in and then there's a rock in the wrong place so you move it and try again and it happens again. And when I was at Denali the camp sites are like a raised garden bed filled w gravel, that was really a PIA to stake out.
This sounds like I'm ragging on the tent, but I'm not, if I had to buy it again I would. But again, that 1 lb tent is not as livable as a 3-4 lb dome tent w a fly. IMHO