Why You're Cold at Night (And It's Not Your Sleeping Bag)

The ground is stealing your heat

A sleeping bag works by trapping a layer of still air, but underneath you that insulation is crushed flat and does almost nothing. Cold seeps up from the ground by conduction all night.

The fix is your sleeping pad's R-value — its resistance to heat loss. For three-season use aim for R-4 or higher; for winter, R-5+ or two pads stacked. Upgrading a pad fixes more cold nights than upgrading a bag.

Damp insulation barely insulates

Loft is warmth. Moisture — from sweat, from breathing into the bag, from a humid tent — collapses that loft. Never bury your face in the bag to breathe; the moisture in your breath condenses in the insulation.

In the morning, air the bag out before packing it. Multi-day trips lose warmth night over night as unaddressed moisture accumulates.

A cold body can't heat a warm bag

Your bag doesn't make heat; it traps the heat you produce. Go to bed already warm — do a few squats, put on a dry base layer, and eat something with fat before sleep so your metabolism has fuel to burn overnight.

A dry hat and a full water bottle of hot water at your core do more on a cold night than a heavier bag would.