I've never slept in my ThermoLite 2.0, but it's seen a little use. My daughter bundled up in it at some of her dance team's events. We'd be out there in 40-ish degree weather with her wearing a dance costume that was never designed to provide warmth.

All the other kids would be trying to share a blanket or two and shivering, my daughter would be in the Bivvy in a camp chair all toasty.