OMM's Core Zipped Vest

Preface

As always, we're looking at the OMM Core Zipped Vest from the point of view of long distance trekking over tough terrain.

Test subject: Chest 42", Waist 33", Height: 5ft 8"
Test item: 2025 version, size = Large
Kit Tests: Spring, Summer (Winter upcoming)
Disclaimer: None required (item not provided by manufacturer)

Datasheet

Manufacturer's Page

 

Scramble Review

Contents

• Introduction: Another Categorical Shift
• Utility Thermal Booster
• Material: Primaloft ACTIVE
• Features
• Any Negatives?
• Conclusion, Rating & Product Images

 

Introduction: Another Categorical Shift

In our Scramble News, April 2025 we wrote about our decision to alter two categories in our review catalogue. One such change was the shift from "Lightweight (~250g) Down Gilet" to "Utility Insulation Layer (Active & Static)":

Our use and subsequent Special Mention review of Marmot's Alt HB Pullover got us thinking about how we should handle our "Gilet" option which was becoming an increasingly redundant "legacy" category as it no longer accurately conveyed our approach. Recently, we've been packing less specialist, lightweight thermal layers that not only boost insulation for the static user (around camp or in a sleeping bag) but also work, in extremis, when active.

Materials like Teijin Frontier's Octa-Yarn, Polartec's Alpha Direct and Primaloft's ultralight ACTIVE insulation (an open synthetic plume woven through a knitted mesh) allow heat to escape when combined with an air-permeable softshell (or no shell at all) yet trap heat when worn under a traditional tightly woven fabric like those used in wind-tops or insulated (belay) jackets.

The most promising item we've come across in this category is OMM's ultralight (140g, size L) Core Zipped Vest which is 35% lighter than the down gilet we had previously recommended and nearly 40% lighter than Marmot's Alt HB pullover which prompted the shift in our outlook.

I've used the OMM Core Vest on the last two kit tests and it's quickly become an ideal pack-in-case item.  We regard the Core Vest as an ultralight, highly packable, insulation booster, utility layer that can play a role whether static or active, asleep or wide awake.
 

Utility Thermal Booster

In essence what all these "open insulations" are doing is taking the fleece to its logical extreme.  The classic fleece + windbreaker worked because the fleece alone was a breathable insulator and so allowed heat to escape, but when paired with an impermeable layer the fleece trapped the air and kept the wearer warm. With Primaloft ACTIVE, instead of a fleece you have a much more compressible "plume" of exposed insulation.

The one negative for such "open insulations" is that they're inevitably more delicate than a traditional, more tightly woven fleece. On the flip-side, they're also a hell of a lot lighter (warmth-to-weight-wise). 

OMM's Core Zipped Vest is a straight forward gilet with a high neck and a single chest pocket. There are no hand pockets. Fell runners who use this as an outer layer don't need them and we recommend the Core Vest (for long distance load carriers) as a utility mid-layer, worn under a softshell when active or a traditional insulated jacket (or sleeping bag) when static. So no pockets, in our view is a sensible move on OMM's part.

OMM's Core Zipped Vest, left to right: front, back, inside-out (front view).

Material: Primaloft ACTIVE

Primaloft ACTIVE is made from a synthetic plume of polyester microfibres (similar to traditional insulation) which is then woven onto a knitted mesh creating a high volume (lofted), open structure; an extremely air-permeable, ultra-fine pile.

Whether the insulation is synthetic sheet, plume or natural down, traditional thermal jackets (like houses) sandwich their insulation between two walls - an outer face-fabric and an inner "down-proof" lining. "Open insulations" like Alpha Direct or Primaloft ACTIVE let the wearer decide what to do with all that heat they've generated:  whether to trap it (under a windproof layer) and stay warm or let the heat dissipate.and the wearer cool down. In essence, these open insulations have modularised (if that's a word) traditional insulation. 

Pictured below (pic #1) is the outer face of the OMM Core Vest, the ultrafine pile in all its plumy, air-trapping-potential, glory. On the right (pic #2), is the inner fine mesh onto which the plume is woven (click the image for a closer look).

A close up view of the OMM Core's Primaloft ACTIVE insulation.

OMM designed the Core Zipped Vest as an active outer layer for fell runners (not an accessory to carry-in-case but as something to wear on the move). The highly air-permeable structure dumps heat, keeping the runner cool, but when static, the runner can quickly don an ultralight windtop such as OMM's own Sonic Smock (~60g) or Montane's Featherlite Nano (~55g) and suddenly they're wearing something very close to a traditional lightweight insulated jacket and keeping warm (for a total of around 200g, and only 60g carry-weight).  You can see the appeal for competitive runners.

Running and long distance trekking have some things in common but also many differences. One difference is that these fell-runners aren't carrying 10 days of food supplies and 50L+ packs. Scramble don't recommend using the Core Zipped Vest as an outer layer. Instead, for our purposes, OMM's Core Zipped Vest has three main roles:

1. Active:  Under a softshell in punishingly cold conditions
   Where resorting to some form of synthetic insulation whilst on the move has been helpful. Such occurrences, at least for me, have generally been at the end of long days, in persistent cold, wet and stormy conditions, when I'm tired, feeling sorry for myself and thinking primarily of where I can pitch to end the misery.
2. Static: Under traditional insulated jackets
   When static (after pitching) in cold conditions, worn over sleepwear to provide a boost to standard insulation pieces.
3. Static: Under a sleeping bag
   Worn over sleepwear (baselayer) when the choice of sleeping bag has been overly optimistic and a thermal boost has been necessary.

In the image below, my top half (minus the hat) is modelling the sleepwear I used on the last two kit tests: the OMM Core Gilet over a Montane Allez Micro Pull-On. It was cool, windy and wet and in such circumstances the Core does make a minor difference; put a windtop over it and the thermal effect is notable.

Let the heat go with the OMM's Core Zipped Vest exposed to the elements.

Features

In terms of features the Core Zipped Vest uses a reverse coil YKK zip (pic #2, below right), has a snug fitting collar and a well-sized chest pocket (pic #1, below left).  That's really about it.  Everything works as it should; no complaints in terms of form, fit and function.

Aside from a chest pocket, there are hardly any features to speak of.

There are a few ultralight gilets in the same weight range that would provide more warmth: Haglofs now discontinued (but still available if you shop around) L.I.M Barrier Vest and OMM's Rotor Vest, both of which use Primaloft Gold Crosscore 40g (Aerogel infused, equivalent to ~60g Primaloft Gold) and weigh around 140g (size Large).  However, in our opinion, neither of these are suitable for active use and thus don't have that "utility" element to them.  They're limited in the same was any insulated jacket would be (when active you overheat and sweat, which is not good in sub zero conditions).
 

Any Negatives?

To date there aren't any negatives.  However, the concern (as it is with most of the "open insulations") is durability.  Time will tell, but most of the negative comments we've seen relating to such items is when they've been used as outer layers. As with most ultralight pieces, we always recommend taking good care of them so they can take good care of you.  The OMM Core Zipped Vest is no different in this regard.
 

Conclusion & Rating

The OMM Core Zipped Vest is the kind of item that you'd throw in your pack if you felt you might be pushing your luck on the thermal front. Unsure or what exactly might be overcome by conditions (sleeping bag, insulated jacket, active layers), you just want something that could slot in to your existing layering to take the edge off, whether active in punishing conditions or static and just feeling the chill.

The OMM Core Vest is an all-round, thermal booster, utility piece, that most importantly can be worn when active without causing you to over-heat and sweat profusely.

Unlike a fleece, the Primaloft Active insulation (an unconfined sheet insulation analogue) lofts and compresses like a high-end insulated jacket; so the OMM Core Vest takes up very little pack space. Yet, like a high-end tech fleece, the Core Vest is extremely lightweight and very air permeable, allowing heat to escape when active. 

At Scramble, we're not big on the whole mid-layer / fleece concept.  However, we aren't against having add-on pieces that can provide a thermal boost when conditions turn toward the unexpected and one's overly-aggressive insulation budgeting is exposed. OMM's Core Zipped Vest is just that, an ultralight add-on that can play multiple roles and it's our top pick in the new "Utility Insulation Layer (Active & Static)" category.
 

Product Images

 

Rating (out of 10)

* The value score is derived from two factors:
1) Competitive Market Price (CMP). This represents our judgement of a competitive online price point if we were to stock the item. e.g. if we feel we would need to sell an item at 40% off (i.e. 60% of its full RRP) to be competitive, then our CMP score will be 6/10.
2) Customer Value Price (CVP). We then make an honest appraisal of the maximum price we would be willing to pay for the item (and we're mean). So if we'd pay 80% of its RRP our CVP score would be 8/10.
We then average the two scores to get our final value score, which in our example would be 7/10.

 

Last Updated: 01/01/26