That's my understanding as well. I have two of the emergency bivys but they are not vented. I haven't picked up the Escape yet but it looks like it has Velcro closure vents on the sides? If I have a few miserable nights I'll be upgrading the system in the first month on the trail but I think the 30 degree bag with the fleece liner will handle march and April. I'll have the Escape bivy in my pack till I find out how right, or wrong I was about my gear choices!