1. A method for analyzing movement of a fluid in an absorbent article that comprises fluid-swellable composite material, which comprises a fluid-swellable solid material, to determine the performance of at least one feature of the absorbent article, said method comprising: inputting one or more properties for said fluid-swellable composite material or fluid-swellable solid material thereof into a virtual model of the absorbent article to produce a representation of at least one feature of the absorbent article; and evaluating, using a computer, the virtual model of the absorbent article to determine the performance and of the at least one feature of the absorbent article, wherein the virtual model comprises a solution to the equations ∂ m 1 ⁡ ( x , t ) ∂ t + ∂ ∂ x ⁢ ( D 1 ⁡ ( m 1 ⁡ ( x , t ) , m 2 ⁡ ( x , t ) ) ⁢ ∂ m 1 ∂ x + D 2 ⁡ ( m 1 ⁡ ( x , t ) , m 2 ⁡ ( x , t ) ) ⁢ ∂ m 2 ∂ x ) = - f ( S ⁡ ( m 1 ⁡ ( x , t ) , m 2 ⁡ ( x , t ) ) · τ · C AGM · A 0 · m max - m 2 ⁡ ( x , t ) m max ⁢ ⁢ and ⁢ ⁢ ∂ m 2 ⁡ ( x , t ) ∂ t = + f ( S ⁡ ( m 1 ⁡ ( x , t ) , m 2 ⁡ ( x , t ) ) · τ · C AGM · A 0 · m max - m 2 ⁡ ( x , t ) m max , ( 1 ) and wherein the solutions are used to develop, an absorbent article.