I will make an observation based off of recent experience, if you're not using a tarp. If it's warm (60dF or warmer) and weather (precipitation) dictates you must zip the bivy to stay dry, it's going to be a hot box lol! If you can keep it open, or just the mesh closed, you'll be fine. I would definitely recommend pairing with a minimal/small tarp and maybe trekking poles, that way you can ventilate/regulate for comfort no matter the weather.