Arc'teryx Phase SL Zip Neck

The Arc'teryx Phase SL Zip Neck weighs 110 grams and dries faster than any other baselayer I've used. Phasic SL fabric, 100% polyester, sits tight against skin and pulls sweat off your body before you notice it's there. The deep front zip and tall collar give you ventilation options during stop-start activities like ski touring and trail running. Priced around $75-85 with UPF 25 sun protection and silver ion odor control. The SL stands for Superlight, and at 110g, it earns that name. Sizes S through XXL in men's, XS through XL in women's.

Phasic SL Fabric and Silver Ion Odor Control

Phasic SL uses a specific knit construction that spreads moisture across the entire garment surface. During hard efforts, sweat disperses broadly rather than pooling in one spot. When you stop moving, that thin film of moisture evaporates quickly, which keeps you from getting chilled during rest breaks.

The silver ion treatment handles odor better than untreated polyester. I've worn this on back-to-back days during backcountry trips without developing the funk that cheaper synthetics pick up after a single hard session. The treatment holds up through repeated washing, unlike spray-on alternatives that fade after a few cycles. The Rho LT Zip Neck uses a different approach with Polygiene, but the Phase SL's silver ions perform similarly for multi-day odor management.

How Does the Arc'teryx Phase SL Zip Neck Fit?

Tight. That's the point. The Phase SL sits directly against skin for maximum moisture transfer, and any looseness undermines the whole design. At just over 6 feet and 165 pounds, I wear a medium that follows my torso without excess fabric. The gusseted underarms prevent binding during arm swings, and the flatlock seams sit flat enough that I don't notice them during long runs.

The tall collar provides moderate neck coverage without feeling restrictive. The deep zip opens far enough to dump heat fast when you're working hard uphill. Mechanical stretch in the fabric allows full range of motion without the gradual degradation that elastane-based stretch develops over time.

Best for 45-65°F During High-Output Activity

This works between 45 and 65°F when you're moving hard. Trail running, ski touring, fast hiking, cycling. The silkweight construction provides almost zero insulation on its own, which sounds like a drawback until you've overheated in a heavier baselayer during a sustained climb.

Below 45°F, I wear it under a fleece like the Kyanite AR or the Dallen Fleece. Above 65°F, I switch to a short-sleeve option. The Phase SL targets that specific window where you need moisture management more than warmth, and it handles that job better than anything heavier.

Durability Trade-offs at 110 Grams

The silkweight construction snags easier than heavier baselayers. Rough pack straps and sharp zipper edges on shells can catch the thin fabric. I haven't torn mine, but I've seen small pulls develop after a few seasons of regular use. Careful handling matters more with this piece than with something like the Pelion Comp LS, which uses nylon reinforcements in high-wear zones.

The fabric maintains its moisture-wicking performance throughout its lifespan without degradation. The mechanical stretch holds up better than spandex-based alternatives because there's no elastane to break down over time. Wash it regularly and it'll keep performing, even if it develops cosmetic wear.

Arc'teryx Phase SL vs. Patagonia Capilene Cool Lightweight

The Patagonia Capilene Cool Lightweight Zip Neck uses recycled polyester at a comparable price. The Patagonia fits slightly looser and uses a different knit pattern. Both dry fast. The Phase SL edges out the Capilene in moisture dispersion speed during sustained high-output efforts, though the difference is marginal during casual hiking.

Smartwool's Merino 150 costs about the same and provides natural odor control with a softer hand feel. The merino dries noticeably slower, which makes it a poor choice for activities with variable intensity. Pick merino for moderate effort in cool weather, pick the Phase SL for hard efforts where sweat management prevents chilling.

The Rho LT Bottom pairs well for a complete baselayer system when you need more warmth below the waist. Check Arc'teryx for current availability.