The Sea to Summit Trek TkII is a versatile, roomy tapered rectangular sleeping bag. A wrap-around zipper make it deployable as a quilt in warmer weather, but in its standard sleeping bag configuration, the bag and its weather-resistant down insulation achieve a 3-season worthy 18 degrees F temperature rating. Renowned for their efficiency in retaining heat and compressible properties, the feathers and fibers of down have an incredibly soft, comfortable feel and, despite advances in synthetic materials, continue to provide the best warmth-to-weight ratio of any insulation available. The one inherent weakness of down insulation is that it loses much of its ability to maintain warmth when it gets wet, but the 650+ RDS-certified fill Ultra-Dry Down featured in the Trek TkII performs differently. Ensuring consistent thermal performance, a hydrophobic treatment enables the insulation to stay dry longer and dry faster if it should become wet than traditional down insulation. This bag uses both horizontal and vertical baffles to prevent down shifting towards the sides of the bag during sleep and the side block baffle construction maintains the 60/40 upper-to-lower fill ratio. The three-dimensional sidewall baffles ensure that the down can loft to the very edge of the bag. The adjustable 3D hood and draft tube help retain warmth. A full-length anti-snag side zipper and secondary footbox zipper offer ventilation and allow the Trek to be laid out flat and used as a quilt. An interior pocket stows small valuables and an Ultra-Sil compression stuff sack is included with each bag. The Sea to Summit Trek TrII sleeping bag is available in your choice of Regular (fits to 6’ 0”) and Long (fits to 6’ 4”) size options.