Furnace Henley

The First Lite Furnace Henley aims to be a high-output base layer, and it largely delivers. It's constructed from their proprietary Furnace merino-X knit, which is a blend designed for warmth without excessive bulk. The fabric has a waffle-grid pattern on the interior, a common and effective design choice to trap warm air close to the body while allowing moisture to escape through channels. This construction makes it suitable for activities where you're generating a lot of body heat but still need insulation when static. The fit is athletic without being restrictive, which is important for layering under other garments.

In the field, the Furnace Henley performs as expected for a quality merino blend. The wool's natural odor resistance is a significant advantage on multi-day trips, and its ability to retain warmth even when damp is a well-known merino trait that holds true here. The Henley design, with its button-up placket, offers decent ventilation control, allowing you to dump heat quickly when working hard uphill and then batten down the hatches when taking a break. It's not the absolute lightest base layer on the market, but the trade-off is superior warmth-to-weight compared to synthetic alternatives in this insulation class.

Durability-wise, the Furnace Henley holds up well. Merino can be prone to snagging or pilling with heavy use, but First Lite's Furnace fabric blend seems to mitigate some of that. While it's certainly more expensive than many synthetic options, its performance characteristics – especially in terms of warmth, breathability, and odor management – justify the cost for serious outdoorsmen. It slots in as a robust, mid-weight merino base layer, positioned for cooler to cold conditions where consistent warmth and moisture management are critical, setting it apart from lighter merino or less breathable synthetics.