1) Insulate inside. Sleeping bag liners (silk, synthetic, or wool) can add 5 to 25 degrees of warmth.
2) Insulate below. Use an inflatable pad to keep you off the cold ground, and layer foam on top to keep body heat close.
3) Stay dry. Lay raingear over your bag to shield it from frozen condensation. Avoid exhaling inside your coccoon—moist breath will leave it damp.
4) Shake it out. Clumpy insulation leaves cold spots. Let your bag fluff out a half hour before bed. Once in, shake your legs to evenly…