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Seirus Heatwave Mapped Base Layer Top

A one-quiver base layer that helps you regulate your temperature while skiing thanks to an innovative, three-fabric mapping technology.

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Seirus Heatwave Mapped Base Layer Top, MSRP, Women’s: $135 [BUY NOW] MSRP, Men’s: $130 [BUY NOW]

After years of donning Merino as a first layer, I was a little wary at first of Seirus’ Heatwave Mapped Base Layers. The new next-to-skin lineup is made from the brand’s Heatwave fabric, used largely in their popular and effective glove liners, but never before in a head-to-toe base layer set. Needless to say, keeping hands warm and dry is quite different than the thermo-regulating needs of a base layer. Would Heatwave be up to the challenge?

I tested the women’s base layer top over a series of early-season days in Colorado’s Front Range, where temperatures started out at around 5-8 degrees and topped out in the mid-20s, with one day never even getting into the 20s thanks to consistent cloud cover and flurries. First impression upon slipping on the base layer top, I was pleasantly surprised by the soft material next-to-skin. This brushed MaxWick serves up that initial warmth to prepare us for the day ahead, and will help to wick away any moisture as the day progresses, keeping us warm and dry.

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The men’s Heatwave Mapped Base Layer Top employs a combination of three fabrics to keep you warm, dry, and comfortable.Courtesy of Seirus

The concept here is that these mapped layers would be the only layer skiers need beneath a jacket thanks to three different types of materials used in various places according to where we get cold, where we perspire, and where we need a little more movability. The reflective Heatwave technology allows the fabric to harness body heat, so these warmest panels are places where we get the coldest: outside of the arms, chest, lower back. The soft-brushed MaxWick can be found where we need a little warmth, but are also likely to collect moisture when we get moving, such as the upper back and abdomen. Finally, an antimicrobial Polygiene mesh is used in the spots that require the most ventilation, such as the underarms. The goal: One layer that understands how your body operates in cold weather and responds in kind.

On a moderate day at Arapahoe Basin, I wore the Mapped Base Layer Top beneath a synthetic insulator and a Gore-Tex shell, although I was worried I would be cold so stashed a thin down vest in my pack just in case. A chill set in on the way up the Black Mountain Express, but dissipated on the first lap down once I began to stoke the furnace. It was a sunny day, and by mid-morning I was feeling toasty-warm enough to unzip the top just a bit, dumping a touch of heat for comfort. (The women’s version has a 1/4-zip at the neck, while the men’s does not.) The vest stayed in my pack all day. On a colder, overcast day, I wore the Mapped Base Layer Top beneath a slightly heavier down insulator and a shell, and despite worrying I might be cold, stayed comfortable and well-regulated all day, though I never felt the need to dump heat.

At $135, the Mapped Base Layer Top is an investment (the pants are $120 and share the same mapping technology and fabrics), but is a smart choice for skiers who get cold easily, or who prefer not to have to don too many layers when they ski.

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