Sleeping bags in the 10°F to 40°F (-12.2°C to 4.4°C)range are offered in both YFuse (YF) and Ultralight (UL) models. Both will resist light condensation, and both make an excellent choice for 3-season sleeping bags. When it comes to choosing between them, the primary consideration is weight: YF bags weigh an average of 3 oz more than their UL counterparts because the YF fabric is twice as thick (20D for YF, 10D for UL), and therefore more abrasion-resistant. The fill power of YF bags is also slightly lower (900+ fill power for YF, 950+ fill power for UL), which means that UL bags are just slightly warmer than their YF equivalent. If fabric feel is also a consideration, YFuse fabric is a little softer to the touch than the Ultralight fabric. For more detailed specifications on all of our fabrics, check out ourfabrics page.