Same physics as the 3D house model, redrawn as a to-scale wall cross-section with its own temperature profile — a more natural 2D view of steady-state 1D conduction than an isometric house. Heat crosses each layer in series (Fourier's law, steady state):
R_total = 1/h_in + Σ(t_layer / k_layer) + 1/h_out
U = 1 / R_total [W/m²K]
q = U · (T_in − T_out) [W/m², heat flux through the wall]
Q = q · A [W, for a 100 m² wall]
Layers modeled (indoor → outdoor): 12.5 mm gypsum board (k=0.17), your chosen insulation, and a 100 mm brick veneer (k=0.77). Interior film coefficient h_in = 7.7 W/m²K. Exterior film coefficient rises with wind speed v via the McAdams correlation h_out = 5.8 + 4.1·v.
Because the flux q is constant through every layer at steady state, the temperature drop across each resistance is simply q·R for that resistance — a straight line inside each solid layer, with the slope inversely proportional to that layer's conductivity. That is what the lower T(x) chart plots directly: each layer's boundary temperature is computed from the running sum of q·R, giving the same physically-real profile an infrared camera would show across a real wall.
- Material / thickness — sets the insulation layer's resistance t/k; a lower k or thicker layer flattens the profile's slope inside that layer and lowers U.
- Outdoor temperature — sets the driving ΔT = T_in − T_out, scaling the whole profile's total drop.
- Wind speed — raises h_out, steepening the small drop right at the outdoor surface (thinner boundary layer).
- Interior surface temperature — the temperature the inside wall surface itself sits at; when it drops within a few degrees of typical room dew point (~12 °C), condensation and mold risk rises even though the room air itself stays warm — a detail the aggregate U-value alone hides.
Particle density and speed crossing the layers scale with |Q|, exactly like the 3D model's exploded wall — same formulas, same numbers, just paired here with the temperature curve that produces them.