This investigation evaluates the changes in web structure of impulse pressed paper webs. 60 g/m2 wet paper webs made from two stock types (SBK and a 60:40 mixture of SBK with HT-CTMP) were pressed either on laboratory scale or on a research paper machine. The pressing temperature was increased stepwise from 40°C to 290°C. The sampled wet paper webs were either dried in restraint in an oven, freeze-dried, or stored in sealed plastic bags at 4°C. Paper samples were obtained both before and after the pressing event, and the evolution of the cross-sectional solidity profile and transverse permeability was measured as a function of pressing temperature. Delamination was first observed at a pressing temperature of approximately 230°C. For non-delaminated paper webs, the cross-sectional solidity profiles translated uniformly towards higher solidities with increasing pressing temperature. We found no evidence of stratification. For delaminated sheets, however, large fractures were evident, with the damage plane located approximately 1/3 of the way in the total basis weight of the sheet, measured away from the hot surface. The permeability of unloaded samples decreased monotonically with increasing pressing temperature reflecting the fact that the paper samples densified by reduction of the external pore size. The permeability of mechanically compressed, never-dried samples was found to be essentially constant for non-delaminated sheets and to increase significantly for samples which were delaminated. We propose that this phenomenon could be a result of cell wall damage incurred during the delamination process.