13 December. Went for a 6 mile run this evening.
Conditions: 16 F, light winds, dry.
Clothing worn (torso): lightweight polyester tee (next to skin), Thorofare shirt, and full-zip single-layer wind jacket
Heavy exertion in these temperatures is usually a game of constant fiddling with layers, of starting off cold, eventually finding a metabolic sweet spot, and ultimately losing it to sweat-induced chilling. Not so tonight, and I believe it had everything to do with my inclusion of the Thorofare shirt instead of a second thermal layer beneath the wind jacket.
A little background: I find a wind jacket, or windshirt with decent ventilation options, essential when exerting in these temperatures, regardless of any wind, since I'll generate my own. Heavier shells, or softshells, don't offer the same versatility. A thin, wicking layer, or several layers as needed, beneath the wind jacket, can be added or removed as necessary, but the jacket is a mainstay.
With the Thorofare in the mix, I started off warmer than usual, apparently as the windshirt-like quality of this shirt afforded some additional protection against convective heat loss, such as at the jacket zipper, cuffs, and perimeter. As I continued to exert, I heated up and eventually began to sweat, per usual. This is when I'd normally consider shedding a thermal layer, both to control sweating and in anticipation of further metabolic warming. Because sweating is impossible to avoid in this scenario, no amount of fiddling with layers will keep the next-to-skin layer dry. A VBL is impractical, so typically it's a case of accepting that moisture will spread from the base layer outward, and ultimately through the wind jacket; that the wind jacket will help control convective and evaporative heat losses to an extent; but that those heat losses will still occur, and ultimately no amount of metabolic warming can forever keep up with the constant sweat-induced cooling.
On a winter hike, I'd also slow the pace in an effort to control sweating. But on a recreational run in the safety net of my own neighborhood, sweat happens. And this is a good thing for testing purposes, at least.
With the Thorofare shirt, I sweat, same as usual. Yet I never felt compelled to adjust my layering, as the sweating never grew intolerable the way it would have with a comparably worn knit or light pile layer. The Thorofare lacks heat-trapping loft, yes, but again it's not a suffocating VBL either. Even better, for the first time in memory I was able to avoid the standard late-run chills, as the Thorofare all but prevented my sweat from migrating to the outermost layer as liquid moisture and evaporatively cooling me. The outside face of the Thorofare, like the shell jacket layered above it, remained bone dry throughout the run.
This lack of wet-out of the outermost layers is an incredible advantage here. It's not something a vapor barrier could ever deliver comfortably while running. A waterproof-breathable shell would likewise have grown intolerable under prolonged heavy exertion. So the Thorofare would seem to be in a category all its own here, passing sweat as water vapor with relative ease while preventing the dreaded wet-out that's the bane of cold weather activity. Duly impressed here in December!
