Arc'teryx Calvus Cap
The Arc'teryx Calvus Cap (Model #17151) weighs 50 grams (1.8 oz) and features Socora polyester fabric, Polydel mesh side panels, and a Spacermesh sweatband for breathability and moisture management. Designed for mountain training and trail running, this features a six-panel build with a short brim, an adjustable TPU strap with a low-profile buckle, and DWR treatment for light rain protection. The Delta knit back panels provide ventilation and antimicrobial odor resistance. Original MSRP was CAD $40 (around $55 USD at current retail). The foam-inserted brim maintains shape without adding weight. I run in the Dallas sun, and this cap is the only thing between me and skin cancer. Arc'teryx categorized it under Training/Fitness and Running, and Wayback Machine captures show a 4.5-star rating across 121 reviews on arcteryx.com.
Socora Polyester and Ventilation
The Socora polyester fabric is light, air permeable, and wicks moisture during high-output activities. Polydel mesh side panels add ventilation zones that increase airflow. Delta knit back panels contribute breathability while the antimicrobial finish prevents odor development during extended wear.
Spacermesh sweatband wicks moisture away from the forehead. This keeps sweat out of my eyes during runs, eliminating the need for constant wiping that interrupts my pace. The sweatband creates space between fabric and skin, enhancing airflow.
Brim and Fit
The short brim provides sun protection without excessive length that catches wind or blocks peripheral vision during technical trail sections. Foam insert maintains brim shape after the cap gets packed flat. The stretch closure strap with a low-profile quick release buckle adjusts for a secure fit across S-M and L-XL sizes. The strap locks without slipping during movement, and the low-profile buckle prevents uncomfortable pressure points.
Weather Protection and Durability
DWR treatment prevents light rain and drizzle from making the cap waterlogged. The treatment causes water to bead and roll off rather than soaking into fabric. The cap retains its shape after multiple washes. The Socora polyester resists pilling and color fading. The foam brim insert maintains structure even after being compressed flat during packing.
How the Calvus Cap Compares to the Sinsolo
The Sinsolo Hat offers more comprehensive sun protection with its bucket-style design and UPF 50+ rating. I switch to the Sinsolo on scorcher days or desert hikes when maximum coverage matters more than the streamlined profile. The Calvus Cap works better for running because its fitted design stays secure without chin cords, while the Sinsolo's bucket-style creates wind resistance. For casual hiking or beach time, the Sinsolo wins. For trail and road running, the Calvus delivers.
Black, Firoza, and White
Arc'teryx offered the Calvus in at least three colorways: Black, Firoza (a bright teal/cyan), and White. The Black is the most common on resale. Firoza stands out as one of the few bright running cap colors Arc'teryx produced. White works for hot conditions where darker fabrics absorb more heat.
Packability and Storage
At 50 grams, the Calvus Cap easily fits in the Mantis 2 or Mantis 1 without taking significant space. The cap compresses flat, and the brim insert returns to its original shape when unpacked. The lightweight construction makes this easy to clip to pack straps or stuff in pockets during cooler sections when sun protection becomes less critical. The DWR treatment means the cap dries quickly if wet. For cold-weather running, I grab a beanie, but I have tried to get out there in my Wool Ball Cap and ended up a soggy mess.