Is it a crisp camping night and you wish you were just a tad warmer? The Sea to Summit Thermolite Reactor Liner raises the mercury bar for a sleeping bag liner to a new standard (providing up to 14°F or 8°C). This piece is super lightweight because of the hollow core fiber construction, and packs into its own Ultra-Sil® stuff sack. On a warm weather night, this could be a standalone bag, which makes this liner pretty versatile.