We study the compression behavior in the thickness direction of paper using quasi-static pressure cycles from 0–10 MPa. The reversible component of compression agreed reasonably well with
the following equation:
where is the volume fraction (porosity) of compressible pores, and E* is the effective elastic modulus characterizing the compression of the pores. The model can be derived both from the height distribution of pore space and from the general linear relationship between logarithmic strain and pressure. In handsheets, the fitted porosity parameter ranged from 0.13–0.22 depending on sheet density. The values of the elastic modulus E* varied between 4 and 5 MPa. They could even be set constant at ca. 4.5 MPa without a significant loss of model agreement. Our results suggest that the reversible compression behavior of paper depends primarily on the porosity of the fiber network and only a little on the furnish composition.