If having the lightest possible jacket is your goal than this might be it, however other super-light jackets, like the Mountain Hardwear Ghost Whisperer Down Hooded for example, weigh only a couple ounces more, and provide features many people deem necessary — a hood, zippered hand pockets, and the ability to stuff the jacket into its own pocket.
For the ultimate in lightweight warmth and wind protection, consider combining this with the Montbell Tachyon Anorak. It is about the most warmth and wind resistance you can get for under 8 ounces.
If you're searching the web for the lightest down layer then consider this — the MontBell EX Light Down Jacket is only 5.6oz… Built with 900 fill down and super-light 7 denier Ballistic Airlight nylon MontBell is aiming for the best warmth-to-weight ratio it can achieve in an extremely light piece. What you have here is simplicity.
The extremely light MontBell EX Light down jacket packs down smaller than all others in our review. Here it is shown packed into its own provided stuff sack.
When you design a jacket that weighs only 5.6oz overall you must do away with almost all features. Building "extremely light," barring magic, entails sacrifice in versatility, durability, and pretty much most standard jacket features. The MontBell EX Light has zero pockets, zero adjustability, and no hood. The final weight savings made here appear to be from that the fact that this jacket has a short fit.
Beyond the provided stuff sack there are almost none - no hood, no pockets, no adjustment cords, this jacket is streamlined to the extreme. The only "feature" here is extreme lightness.
The design of the EX Light Down Jacket is geared to those looking to the extremes of weight savings. If your only concern is extreme lightness then this jacket may be for you, as it is designed to provide a touch of warmth in the lightest way. However, at only 5.6oz the EX Light Down Jacket saves weight not just by foregoing features and using a super-light shell; there is only 1.8oz of down (albeit lofty 900 fill) in this jacket meaning that at the end of the day it's not nearly as warm as the other, higher fill-weight jackets reviewed here. For reference, the Mountain Hardwear Ghost Whisperer Down Hooded jacket weighs 7.5oz, has 2.78oz of 850 fill down and has a hood and pockets. If you're a climber, consider that the EX Light comes with a stuff sack and does not stuff into a pocket and clip to a harness.
For about $200 you can get an extremely light jacket. What you are paying for is 900 fill down and the vision of simplicity. What you don't get is features. If you are looking for a more versatile, warmer and more durable jacket, look to the MontBell Frost Smoke Parka which is priced similarly. Other more versatile options are the Feathered Friends Hyperion, Patagonia Ultralight Down Hoody, the MontBell Mirage Parka, MontBell Frost Smoke Parka, and the Mountain Hardwear Ghost Whisperer Down Hooded.