I haven’t used the full zip but pretty much echo this entirely. I hype the ambient to any friend that will listen. It performs a lot better than a nano air, etc for me being faced only on 1 side. I’m rough on it as it’s held up pretty dang well. Still not using grid fleece over using the ambient.The Ambient Hoody is my favorite, most versatile, best performing, and downright comfortable mid-layer / active insulation piece I have used. Saying "must" is a stretch, since we could all live with something not as nice and still enjoying the mountains. I am not a fan of the Ambient (full zip) jacket, as I find it too warm for MY needs.