How do radiation shields reduce heat transfer and how is their effectiveness calculated?

Radiation shields are low-emissivity surfaces placed between hot and cold surfaces to reduce radiative heat exchange. Each shield creates additional resistance. For N shields between parallel plates, heat transfer reduces to: Q_with_shields = Q_without_shields/(N+1) for shields with same emissivity as surfaces. For different emissivities: each shield adds resistance of (1/ε₁ + 1/ε₂ - 1). Example: polished aluminum shields (ε=0.05) are highly effective in cryogenic applications, vacuum flasks, and spacecraft insulation (MLI uses multiple reflective layers). A single shield can reduce radiation by 50% or more depending on emissivities.