Arc’teryx’s Delta Jacket is an ultralight fleece made of Octa Fleece, one of the newer, high-tech fleeces to hit the market in the past couple of years. The name comes from the octopus-like weaving which creates air gaps, which help trap warmth while also allowing moisture to escape. It’s very popular with cottage industry ultralight brands, but Arc’teryx adopted it for the 2025 revamp of the company’s popular Delta fleece jacket.

I hesitated to put this jacket in this guide because, while I like it as an ultralight mid layer for summer trips, there is an older, heavier version of the Delta jacket. Judging by the angry reviews on Arc’teryx’s website, it was very popular. This jacket is something else entirely, but disgruntled fans of the older version aside, this is a great mid layer for summer trips, especially when paired with a sun shirt hoodie. At 8.5 oz for this, and 6 oz for a sun hoodie like the one from Kuiu below, you have a combo that allows multiple layering options and still weighs less than many more popular grid fleece options. My only gripe is that fashion was, um, not taken into consideration in the design of this jacket. One user review on the Arc’teryx site likens it to Mr. Roger’s sweater, which is about right. But hey, it’s light, it’s functional—who cares about fashion in the backcountry?