JMT Ultralight Sweater

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

At 7 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. Designed for summer layering in the mountains, it's named after the classic John Muir Trail in the Sierra. View it as an insulated windbreaker.

Also available in a warmer version.

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. 


The JMT Sweater is trim and devoid of clumsy features. It is best applied as a windproof, warming layer over one or two thin thermal shirts.

Additionally, the JMT can be put to use as extra core insulation while sleeping, thus making a lighter sleep system possible.

This is not an 'Active Insulation' layer. However the JMT would make a great companion piece to this new breed of outerwear, such as the Patagonia Nano Air Light, for comfort at a full range of conditions with very little weight and bulk. 


This is a simple jacket, lean on features, with the focus being 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. The latter saves 10g, but can also prolong the life of the garment while making it easier to handle in strong winds.

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. In fact, for most users, only a very thin beanie will fit under this trim hood.

The chart below reflects the JMT with a hood. Choosing a collar will save 20g depending on size.

We make the JMT Sweater without any exterior pockets. The hood casing have a fixed, pre-tensioned shockcord. The JMT does not have an elasticized waist cord.

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

Synthetic Fill

APEX by Climashield, a superior continuous filament synthetic insulation, is the choice here.

For the JMT Sweater we use 2.2oz/yd - 75g/m Climashield APEX which is light, compact and applicable for 2season use, roughly defined as summer mountains in the western US. With minimal sewn through stitch lines (none on the shell), and substantial loft in the APEX, the JMT is surprisingly warm as well as very resistant to moisture from sweat and weather.  


The JMT can be configured with a 10d shell 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 inside liner is always the breathable 10d. 

10d. Smooth, comfortable and about the lightest material possible for practical shell use, at 0.67 oz/yd. Very breathable with minimal moisture repellency. Also the standard inside liner.


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 Skaha/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. 

Also see here.



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

Currently unavailable.

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

At 7 ounces for a size medium the hooded JMT packs tremendous warmth and function in a small, all conditions package.

Product Options
Jacket or Pullover
The Pullover Style features a half length front zipper, and weighs 10-15 grams less.
Pullover Style, with half length front zipper
Jacket Style, with full length separating zipper
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.
Shell Fabric

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

Liner Fabric
Integrated Hood and Collar Choices
Choose how to finish out the head opening. An integrated hood eliminates a collar.
Regular Insulated Collar
Insulated & Integrated Hood
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.
Yes, please include a stuff sack
No stuff sack