Understand Why the Ground Wins First
The ground pulls heat out of you by direct contact faster than cold air ever could.
Bare ground, damp soil, or a rock or log surface directly under where you plan to lie.
Conduction moves heat out of your body into the ground faster than convection moves it into the air around you — an uninsulated bed can undo an otherwise good shelter.
Treat ground insulation as equal in priority to the roof, not a detail to add once the structure is finished.
Lie on bare ground for one minute — the cold you feel first, at your hips and shoulders, is exactly where a bed needs the most thickness.
Focusing all your effort on the roof and walls while sleeping directly on dirt, duff, or a single thin layer.
Build a Compression-Resistant Bed, Not Just a Soft One
Body weight compresses insulation, and compressed insulation stops working.
A coarse base layer of small boughs, sticks, or bark laid first, then a thick top layer of dry leaves, grass, or needles.
The coarse base layer keeps an air gap under your weight — the top layer alone will compress flat under your hips and shoulders within minutes.
Build the bed until it holds a hand's-width of loft under body weight, not just before you lie on it — press-test it before committing.
Push down firmly where your hip will rest. If you feel the ground or a hard surface through the bed, add material there specifically.
Judging bed thickness by how fluffed-up it looks rather than how thick it stays once your weight is on it.
Cover Your Whole Body Length, Not Just the Middle
A bed that's warm at the hips and bare at the shoulders or feet still costs you the night.
Bed material extending the full length you'll actually lie down, head to feet, not just the widest or most convenient patch.
Heat escapes wherever the ground is exposed, and shoulders or feet touching bare ground will wake you long before the drop feels dangerous.
Build the bed to your full lying length first, then thicken the high-pressure points — hips and shoulders — second.
Lie down fully before finishing the shelter roof. Any bare or thin patch shows itself immediately as a cold spot.
Sizing the bed to the shelter floor instead of to your own body, leaving gaps at the head or foot end.
If you can feel the ground through the bed at your hip or shoulder under full body weight, add material there before doing anything else to the shelter.
Perfecting the roof while sleeping on a thin, patchy ground bed. The ground steals heat faster than the air above you does.
Insulate the whole body length, and press-test before you trust it.