Open-Back Wind Jacket: The Development Story
by Shingo Numata
In the fall of 2026, MUNIEQ launched the Open-Back Wind Jacket, an ultralight wind shell built around an entirely new concept.
As the name suggests, it's a wind jacket with an open back.
The Beginning: A Chilly Trail Running Race
The idea came to me during a late-autumn trail running race.
The course moved between sheltered forest sections and exposed grasslands swept by cold winds. As conditions changed constantly, so did my need for an extra layer. I found myself repeatedly stopping to put on or take off my wind shell, and the process gradually became frustrating.
Then, I tried wearing the jacket back-to-front.
With my running pack still on, I simply slipped my arms through the sleeves and threw it on back-to-front. It was surprisingly easy.
Later in the race, when fatigue set in, even the simple act of reaching behind to put on a jacket felt like unnecessary effort. Wearing it backwards was dramatically easier, and it still provided the wind protection I needed.
However, it created a new problem.
Accessing the front pockets of my running vest and reaching my flasks became awkward and inconvenient.
That realization marked the beginning of the project.
Making Back-to-Front the Right Way Around
What if the back of a jacket became the front?
A few weeks after the race, I discussed the concept with my sewing mentor, Mr.Fukuda of LIAT. He helped create the first prototype using 30D nylon fabric, and I began testing it extensively in the field.
By eliminating the back panel altogether, the jacket could be put on simply by slipping your arms into the sleeves, pulling it over your head, and fastening the waist strap. Just as I had imagined, it was dramatically easier to put on and take off than a conventional wind shell.
But reducing the burden of putting it on and taking it off was only part of the story.
Whether running or hiking, carrying a pack inevitably causes your back to become hot and sweaty. After all, your back is pressed against a highly insulating backpack.
When wearing a conventional wind shell, either under or over a pack, the layering system might feel perfect across the front of your body and arms, yet your back can quickly become soaked with sweat.
Once I started designing around the assumption that a pack would always be worn, I realized something important.
The primary purpose of a wind shell is to protect the parts of your body exposed to the wind. When a backpack is already covering your back, the rear panel contributes very little to that function.
Rainwear is a different matter. A rain jacket needs complete coverage.
But for a wind shell, removing the back panel actually makes it significantly more comfortable and breathable while maintaining the protection that matters.
After spending considerable time testing the concept in real-world conditions, I became convinced of its advantages and began refining the details for production.
Designed for Hiking, Too
Although the jacket was born from trail running, the more time I spent using the prototypes, the more I began to realize that it could be just as useful for hiking. In fact, its advantages became even more apparent on routes with constant short climbs and descents, where body temperature can change quickly.
With the small packs commonly used for trail running, typically around 10 liters in capacity, there are already a few ways to deal with layering. Some runners simply wear an oversized wind shell over their pack, while others choose garments designed with extra room in the back to accommodate one.
That approach becomes much less practical once you're carrying a hiking pack of 30 liters or more.
Every time you need to put on or take off a wind shell, you have to remove the pack first. For hikers who prefer to keep moving rather than stop repeatedly along the trail, that can be surprisingly disruptive. And once the shell is on, the back often becomes uncomfortably sweaty.
Because of this, I designed the back opening with larger hiking packs in mind as well, allowing the jacket to be worn without removing the pack. Of course, compatibility depends on the shape and size of the pack, so I would encourage anyone interested to try it on while wearing their usual backpack.
Once you get used to being able to put a wind layer on and off without stopping, while also eliminating the heat and moisture trapped against your back, it's hard to imagine going back to a conventional wind shell.
Stuff It Into a Pocket
If the jacket can be put on and taken off without removing your pack, it naturally follows that it should be stored somewhere equally accessible.
For trail runners, that usually means one of the front pockets on a running vest. For hikers, I envisioned it being tucked into a side pocket of a backpack.
The front pockets of a running vest don't offer much spare volume, so keeping the jacket as compact as possible became a priority. I looked for the lightest fabric I could find that would still provide sufficient durability and wind resistance. After testing a number of candidates, I settled on a 7D ripstop nylon.
Because the jacket was designed to live in a pocket, I deliberately chose not to make it packable into its own pouch. Instead, I preferred the simplicity of being able to scrunch it up and stuff it directly into a pocket without any extra components.
The fabric is so thin that it is almost translucent, yet it provides the wind protection needed in the field. At just 50 grams (size M), the jacket adds virtually no weight to your kit while ensuring that protection is always within reach.
Designed Not to Blow Away
One thing I noticed during that trail running race was that putting on and taking off a wind jacket in strong winds can be surprisingly stressful. You're constantly worried about the jacket being ripped from your hands and blown away.
To solve that problem, I added an elastic drawcord inside the jacket.
By clipping the cord to a loop or attachment point near your pack's storage pocket, you can put the jacket on or take it off without worrying about it disappearing into the wind.
The cord serves another purpose as well. To make it easier to distinguish the inside from the outside when putting the jacket on, the attachment loops are made in a fluorescent color, providing both a functional cue and a visual accent.
To accommodate different storage preferences, loops are positioned on both sides of the jacket near the waist. Whether you store the jacket in a left or right pocket, a hiking pack's side pocket, or a running vest's front snack pocket, the drawcord can be used in the same way.
A Deep Front Zip
One of the challenges I discovered when wearing a conventional jacket back-to-front was accessing the front pockets of my running vest. The solution was a deep front zipper.
Extending to just below the sternum, the zipper provides easy access to flasks and other items stored in the front pockets without the need to remove the jacket.
The zipper also serves as a simple and effective way to regulate body temperature. Opening it allows additional airflow when conditions warm up, helping to dump excess heat while on the move.
Large Buckles for Gloved Hands
Moving air transfers heat far more efficiently than still air. That's why a strong wind can make you feel cold so quickly.
The moments when you reach for a wind jacket are usually the moments when you're already feeling chilled. Your fingers may be numb from the cold, or you may already be wearing gloves.
With those situations in mind, I deliberately chose relatively large 20 mm buckles for securing the hem behind the waist. While smaller hardware could have saved a little weight, the larger buckles are significantly easier to operate with cold fingers or while wearing gloves.
Final Test: 100-Mile Trail Race
The final test came during a 100-mile trail running race over a September holiday weekend.
I carried the jacket tucked into a pocket of my running vest and successfully covered the full 100-mile distance. My only regret is that I was so focused on getting through the race that I didn't take a single photo.
Races of this kind continue through day and night, often bringing significant changes in temperature and weather conditions. Frequent layer adjustments become part of the challenge.
Over those long hours on the trail, I was reminded just how important it is to be able to put on and take off a wind layer quickly and without stress. For runners who want to keep moving and avoid unnecessary stops, even a small interruption can feel like a burden.
That experience confirmed that the concept worked exactly as intended.
In Closing
MUNIEQ was created from three words: Minimal, Unique, and Equipment.
As the name suggests, our goal is to create equipment with minimal functionality expressed through unique design, offering users new ways to experience the outdoors.
I have to admit, the Open-Back Wind Jacket is a rather unconventional piece of equipment. Unlike a traditional wind shell, it's probably not the kind of jacket you'd throw on for a casual walk around town.
What it offers instead is something no conventional wind shell can: a unique set of advantages made possible by its purpose-driven design.
I hope hikers and trail runners will discover the benefits of the Open-Back Wind Jacket for themselves, and in doing so, find new ways to move through the mountains, whether that's walking farther, running longer, or simply continuing without interruption.
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