Winter van insulation: condensation, thermal bridges, R-value math

Dew point is the rule everyone skips. At 20°C interior with 60% relative humidity (two people breathing on a normal night), air condenses the moment it hits a surface at 12°C or below. In winter, the outer steel panel sits at -5°C and its interior face creeps up to only ~5°C with thin insulation. You're sleeping under a waterfall. Bare Armaflex 19mm gives you R = 0.019 / 0.033 = 0.576, which I round to R ≈ 0.58 m²K/W. Barely acceptable for mild winter (target R≥0.6 walls, R≥0.8 roof). For Scandinavia at -15°C, go R≥1.2 walls and R≥1.5 roof.

Thermal bridges are where 80% of builds fail. Steel has λ = 50 W/(m·K), Armaflex λ = 0.033 — that's 1515× worse. An untreated roof rib becomes a 2°C strip while everything around it sits at 18°C. Result: black mold along every rib within three months. Door frames, hinges, wheel arches, seat rail mounts — all bridges. Fix it by wrapping Armaflex past the edges, using recycled PET fiber batts around ribs, and taping every rivet with aluminum foil tape. Single-glazed windows hit U ≈ 5.8 W/m²K vs 0.5 for an insulated wall — they typically account for 15-30% of heat loss in a standard van conversion (up to 30-50% in poorly insulated builds with large window areas). DIY Reflectix panels with neodymium magnets beat any €200 commercial kit.

Material choices: sheep's wool looks great on Instagram but absorbs 30% of its weight in water and molds within two winters. Spray foam in a van? Never — it off-gasses and cracks from panel vibration. Reflective bubble foil glued flat (Reflectix alone)? Useless thermally. It only works with a 2cm air gap as a radiant barrier, mainly for summer roof heat. The winner: Armaflex AF 19mm (closed-cell, acts as its own vapor barrier) plus Thinsulate or recycled PET stuffing the cavities. Never put a separate vapor barrier behind Armaflex — you'll trap moisture. Floor insulation: skip for weekend use, mandatory for full-timers (cold feet = misery). None of this matters without ventilation (Maxxfan + CO2 monitor). Two people breathe out ~1L of water per night — it has to go somewhere.