Sea to Summit Spark Pro Sleeping Bag

The 15°F rating is an EN/ISO comfort limit, meaning it is designed to keep an average user warm down to that temperature. However, your personal warmth depends on your sleeping pad's R-value, your base layers, and how much you personally feel the cold.

The bag features a side zipper, a footbox zipper, and a half-length zipper on the opposite side. This allows you to vent just your feet, open the top like a quilt, or fully unzip the bag for maximum airflow on warmer nights.

The down is treated to be water-resistant, which helps it maintain loft in humid conditions better than untreated down. While it handles moisture well, you should still use a waterproof stuff sack to keep it dry during transport.

While it is a performance mummy cut, the ergonomic design provides enough room in the shoulders and hips to shift positions. If you are a very active sleeper who needs significant leg room, you might find it snug, but it is optimized for efficiency rather than maximum sprawl.

The vertical baffles on the chest are specifically designed to prevent the down insulation from shifting or migrating to the sides while you move. This ensures the insulation stays centered over your core where you need the most heat retention.

The 10D nylon is chosen specifically for its ultralight weight, so it is quite thin. It is durable enough for standard backpacking, but you should be careful around sharp rocks, sticks, or campfire embers to avoid tears.