JMT Ultralight Sweater

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Minimalist 2-3 season synthetic insulated jacket for light layering, with a short body and generous sleeve length.

At 7.4 ounces for a size medium the hooded JMT packs tremendous warmth and function in a small, all conditions package.

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The JMT Sweater is our lightest insulated shell named after the classic John Muir Trail in the Sierra. 

Built with Climashield APEX, a lightweight yet remarkably efficient synthetic insulator, the JMT will retain some warmth when damp, and will dry and recover more quickly than down. 


This is a simple jacket, lean on features, with the focus on as much warmth for the weight as possible. In its basic configuration the APEX insulation makes up over 55% of the total weight.

The JMT is available with a full separating front zipper or a half length pullover style zipper. 

We build it with or without an integrated hood. The hood option is fully insulated and offers complete coverage to above the chin - but it is not helmet compatible. For most users, only a very thin beanie will fit under this trim hood.

Key design points to take note of:

* The JMT is built with a short body.

* The JMT does not have an elasticized waist cord.

* The sleeve ends are cut trim with no additional closure offered.

Synthetic Fill

2.5 oz/yd Climashield APEX  - 85 g/m - Static comfort to 45°F*

3.6 oz/yd Climashield APEX  - 122 g/m - Static comfort to 35°F*

*A healthy, well acclimatized individual with a full belly and adequate layering, protected extremities, and out of the wind.


The JMT can be configured with a 10d fabrics in a number of different colors. It's an ultralight fabric for folks who want the lightest, but realize that abrasion and tear resistance is minimal.


The stock cut is aimed at providing a short jacket with a trim fit, best when used over only one or two lightweight thermal layers. Compared to the PCT line of APEX hoodies, the JMT Sweater is a size smaller in the torso while the sleeves are the same

The chart and configuration menu below outlines the many options for sizing the JMT Sweater. Tall people may wish to go up in zipper and back length. Likewise, folks with long arms will know when to add to the sleeves. 


Can't go wrong

I've tried several other apex jackets over time, and the fit and hood shape of the JMT sweater are more refined than others - less bulk in armpits without being too tight on the shoulders, and better coverage around my face, along with sleeves that don't ride up my arms. I added 2" to the front and back hem, which as someone with a 'tall' torso (22-23inch measured for a pack) worked out well. I went with kangaroo pocket, 1/4 zip, and the 3.6 body/2.5 arms and can layer with hiking shirt + fleece + JMT sweater and even fit a rain jacket over it all (that's pushing it a bit, but nice to know it's possible) Super warm at rest in the 30s without a midlayer, which is great for altitude or shoulder season. L/XL with these add-on options came in around 11oz


Best Jacket I’ve Owned

I almost never write reviews, but this jacket more than deserves it. I’ve had both a Patagonia Micro Puff and an Enlightened Equipment Torrid APEX in the past, and while they did great with weight, they just were never warm or versatile enough. I did some searching around the internet, and found that Jupiter Hikes did a review on one of Nunatak’s Jackets. Well, after a very easy and quick talk about customization options with Jan, I had a jacket just like his, and guess what; it weighed even less than my last two jackets. I’ve used this particular jacket down to around 25 degrees, and have been very surprised at just how warm it is. If you’re thinking about pulling the trigger, go for it! the weight and the custom options for the price are worth it 100%.



The jacket arrived today.

First impressions are: WOW!

It fits me perfectly. I'm pleased I went for the longer back length and longer sleeves.

The material feels great and the jacket feels warm.

The #5 two way zip is superb - I've never been a fan of lightweight zips. The extra weight for it is so minimal.

The total weight is amazing - 239 grms!

Many thanks for such a superb piece of gear!

Best wishes,

G in the UK

  • 1 out of 1 people found this review useful.


I am very impressed with the JMT jacket I must say.
no frills, all function, truly UL.

  • 1 out of 1 people found this review useful.

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JMT Ultralight Sweater

JMT Ultralight Sweater

Minimalist 2-3 season synthetic insulated jacket for light layering, with a short body and generous sleeve length.

At 7.4 ounces for a size medium the hooded JMT packs tremendous warmth and function in a small, all conditions package.

Product Options
Basic Style

Pullover Style with Hood
Full Zipper with Hood
Pullover Style with NO Hood
Full Zipper with NO Hood
Torso Length
Adds a number of inches to the back and front length of the selected general size.
Sleeve Length
For folks with long arms, or skinny torsos.
Climashield APEX Level

 The lightest in weight offers the least warmth, etc. 

2.5 oz/yd
3.6 oz/yd in body - 2.5 oz/yd for sleeves and hood
Shell Fabric

Please see our Fabric Page for help choosing the right shell material.

Liner Fabric

Hand warmer Pocket Option

Interior Zippered Chest Pocket
With a vertical opening hidden behind the main front zipper, these pockets are protected yet easily accessed.
The pockets adds 16 grams in size large.
Stuff Sack
Our stuff sacks are pretty dope, but current weight saving trends in ultralight circles eschews this once crucial item. So, opt out and save $ while also being very current.
No stuff sack
Yes, please include a stuff sack