Hey Jason,
Great question. I’m not a big fan of half zip rain shells for backpacking, so I’d likely look for something similar in a full zip. The Storm Racer would be a good ultralight substitute, but we’ve grown to prefer rain shells with front hand pockets for backpacking. Hope that helps,

Patagonia no longer makes the full zip M10. Would you still recommend the half zip version of the M10? Have you been able to check out their Storm Racer jacket? Awesome website by the way!

Happy to help!

I use mine all the time with different layers. Sometimes I even use it with just a dri fit t-shirt underneath. It’s good as a windbreaker that way and can also be good in the rain when you need to keep your body temperature down. So no, you definitely don’t need a down jacket with this shell, but I also almost never backpack without one. Summer nights can still get very chilly and I wear my ultralight puffy coat almost every day on the trail. Especially on trails like the JMT where you’ll be at high elevations, nighttimes can get quite chilly. So, this thin shell works great as a raincoat/windbreaker in an outdoor layering system, but it won’t keep you warm on it’s own. You’ll need another layer for that purpose. Hope that helps!

Thank you,
Lance