Women Mammut Swift Ultra Light Cap

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Incredibly light, highly breathable, and easy to forget you’re wearing—this cap was clearly built for moving fast and packing small.

Outdoor Research says: 

The Swift Ultra Light Cap is the ultimate trail running and outdoor training hat, featuring a hybrid-mapped, ultralight design with maximum ventilation for pushing the pace in alpine or on the road.

The Swift Ultra Light Cap’s hybrid-mapped design is made with an ultra-breathable bluesign® approved polyester blend on the top of the crown and 100% recycled polyester on the side panels. The cap is designed to be crushable and packable to stuff into pockets and packs, and the drawcord closure at the back delivers a secure, adjustable fit. DWR finish and UPF 30 protect from the elements, and just the right amount of movement-mirroring stretch provides a precision fit and all-day comfort.

With a firm focus on ultralight breathability and ventilation for fast-moving, high-tempo outdoor wear, the Swift Ultra Light Cap epitomizes lightweight, technical trail running gear.

Our Verdict

Featherlight and effortlessly breathable, the Swift Ultra Light Cap feels purpose-built for fast movement and minimal pack weight. At just 39g in the small/medium size, it all but vanishes once it’s on. The hybrid fabric layout allows the crown to breathe freely while the recycled side panels channel airflow exactly where needed. On steep ascents and muggy mornings, it wicked sweat efficiently and dried out in no time.

The crushable construction means you can stash it in a hip belt or vest pocket without a second thought. The drawcord closure offers a snug, bounce-free fit—even in strong winds—and I appreciated the sleek, no-fuss design that doesn’t scream “technical gear.”

– Reviewed by Ultralight Outdoor Gear

Features

• Breathable
• DWR Treatment
• Movement Mirroring Stretch
• Quick Drying
• Ultralight
• UPF 30
• Water Resistant
• Wicking
• 2025 Updated Fabric
• Crushable
• Drawcord Closure
• Hybrid Mapped Construction
• Packable

Specifications

• Small/Medium Weighs: 39g
• Medium/Large Weighs: 44g

Material & Construction

• Top of Crown: bluesign® approved 86% Polyester 14%
• Spandex Side Panels: bluesign® approved 100% Recycled Polyester
• bluesign® Approved Materials

Help & advice:

• Recycled Content in Outdoor Gear
• The Bluesign System