A New-Generation Shell for Perpetual Motion: Rab’s Phantom Jacket Redefines the Meaning of 'Lightweight'

A shell that's 'just lightweight' or 'just blocks wind and rain' simply won't cut it anymore.

Rab's Phantom Jacket is a waterproof, lightweight shell designed for trail runners, fastpackers, and anyone who needs to keep moving for extended periods with minimal gear.

It performs reliably when you need it and lets you forget it's even there when you don't. This radically minimalist design is a testament to Rab's philosophy of creating 'reliable gear'.

In this article, we sit down with Yuta Yoshino of LandR Inc. to explore the story behind the jacket’s creation, the secrets to its featherlight weight, and its impressive functionality.

The Goal: A Lightweight Waterproof Shell for Uninterrupted Movement

Rab is an outdoor brand born in Sheffield, UK. Since its founding in 1981, the company has drawn from the real-world experiences of mountaineers to pursue stripped-down designs and field-tested, reliable performance.

Its design, steeped in the functional beauty forged in mountain environments, is highly acclaimed by mountaineering enthusiasts and trail runners alike.

The "Phantom Jacket," released by Rab for the Spring/Summer 2025 season, is a lightweight waterproof shell developed to suit the modern pace and style of mountain activities.

"With the recent boom in activities like trail running, fastpacking, and ultra-running, traditional, heavy-duty waterproof shells can often be overkill, restricting freedom of movement. So, Rab set out to develop an emergency shell based on the premise that it would be carried at all times."

"The development process began with 'clearly defining its intended use,'" he says.

"Today's long-distance, long-duration activities with lightweight gear, such as trail running and fastpacking, demand a shell that you can always carry in case of sudden weather changes and quickly put on when needed. With that in mind, we prioritized a comprehensive design that fulfilled three key criteria: lightweight portability, ease of putting on and taking off, and a stress-free experience during high-intensity exercise."

The Fabric Engineering Behind 'Ultra-light' and 'Minimalist'

A major contributor to its portable, lightweight nature is the 7-denier nylon face fabric featuring a Pertex Shield 2.5-layer construction. This is extremely thin for a waterproof shell, keeping the fabric weight down to just 51 gsm.

GSM, or grams per square meter, indicates the weight of one square meter of fabric. The fabric used in this model weighs 51 grams per square meter. When you consider that typical waterproof jackets range from 100 to 150 gsm and even lightweight shells are around 70 to 90 gsm, this 51 gsm figure places it in the extreme class of lightweight waterproof shells.

This wasn't simply a matter of making the nylon thinner; a careful balance was struck to ensure real-world durability by optimizing yarn quality, weave density, and coating design.

While pursuing a lightweight design, the jacket still boasts a water resistance of 20,000 mm and a breathability rating of 20,000 g/m²/24hrs.

"We're anticipating sudden downpours in mountainous areas and on trails, as well as high-perspiration activities. This is a practical level of waterproof breathability, focused on weathering a storm while you're on the move, not for hunkering down in a torrential downpour for hours."

Detailing that Maximizes the Advantage of Being 'Lightweight'

So how did Rab transform this material into a waterproof shell that's both comfortable and user-friendly? The answer lies in the details.

First off, the jacket features a full-length front zipper.

"It adds a fraction more weight compared to a pullover, but we opted for a front zipper to prioritize speedy on-and-off and greater flexibility for temperature regulation. The speed of changing, the ventilation options, and the freedom to manage body heat were more valuable than shaving off a few grams."

The hood is a roll-away design that packs down compactly when not in use. It minimizes flapping while you're running or in high winds, and when you're wearing it, ventilation holes at the back of the head keep you cool.

A key feature of the pattern design is the pre-curved elbows. This design, based on the natural bend of the arm, prevents the fabric from feeling tight or pulling when you swing your arms.

Meticulous attention was also paid to its packability, resulting in a surprisingly compact size.

"We worked on the assumption that you'd be taking it with you every time, so we designed it to be small enough to fit in the pocket of a running vest."

The Model's Name Comes From Its 'Barely-There' Lightness

The Phantom Jacket is designed to be worn over a highly breathable, sweat-wicking base layer. When the temperature drops, just add a thin mid-layer underneath and use the Phantom as your outer shell. It allows for easy layering without restricting movement, letting you adapt flexibly to changes in temperature and weather. While originally intended for high-output activities, many users also wear it for daily life thanks to its minimalist design and functionality.

The model name 'Phantom' embodies the concept of 'a lightness so profound you forget it's there.' It's so light you forget you're wearing it, and it doesn't take up space in your pack. Yet, when you need it, it performs flawlessly. It might be unseen, but its function is undeniable.

For those who don't want to stop moving—whether in bad weather or during high-intensity efforts—the Phantom Jacket will prove to be a completely reliable partner.