@slothrop (funny you ask, I carry a Bluetooth thermometer) I know I’ve used this bivy down to 12F (-11C) many times without issue and no condensation.
The upper nylon is wet proof and has a DWR coating but I wouldn’t use it in rain except for emergency. If there’s fog/mist and chance of dew or frost I just bring a tarp (or more often don’t go out, I like nice conditions).
Also, I use a winter quilt and insulated inflatable when it’s colder (plus down balaclava and booties).