Moisture changes in a paper sheet cause curling and cockling due to expanding or shrinking fibres. Mathematical modelling of these phenomena is considered in this paper. The paper sheet is assumed to be a heterogeneous orthotropic elastic material. Heterogeneity of the paper is handled by dividing it into small pieces, assuming one piece to be homogeneous. This leads to a mathematical model consisting of thousands of homogeneous orthotropic pieces which have different elastic properties and moisture expansion coefficients. The mathematical model is solved using the finite element method. We will show numerical examples and conclude in this paper that the elastic model is able to predict out-of-plane deformations such as cockling of the paper sheet.
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