Affine network model (Kuhn & Grun 1942): crosslinks deform affinely with macroscopic strain. Each Gaussian chain strand contributes to stress. Neo-Hookean constitutive law: σ = G(λ − λ⁻²) where G = νkT is the shear modulus, ν is the crosslink density, and λ is the extension ratio. Increasing λ stretches strands and stiffens the network.