The expansion of paper caused by change in relative humidity was measured on several sorts of papers, microscopically and mechanically.
Changing relative humidity from 5% to 95%, tracing paper made from low freeness stock has high expansivity i.e. 0.9% on Machine Direction, 3.0% on Cross Direction; printing paper of high freeness has comparatively low expansivity i.e. 0.3% on M.D., 0.8% on C.D.
Measurements on series of handmade sheets in varying freeness of pulp have showed that the low freeness-sheets may have high expansivity and vice versa.
It may be recognized that the expansivity depends mainly on amount of its void space between the fibers, because of its cushioning effects. Being increased the density of sheets with beating, the expansivity becomes higher, in spite of decrease of the expansivity of the individual fiber itself.
No significant relations between expansivities of sheet, caused by relative humidity change and caused by dipping into water, have been observed.
It has been generally known that the rate of tension applied on the sheet during its drying process is one of significant factors which affect to physical properties of sheet.
To comfirm the above fact we pressed handmade sheets up to 60% moisture content, and applied several rate of tension on one direction until it was dried up.
The sheets showed less expansivity in tension direction than that caused with no tension while on the cross direction to the tension applied, no appriciable change was
It may be considered that the tensile force during the drying process change the fiber orientation giving distortion to the fiber structure and many other effects.
From above investigations it may be recognized that it is important for design of paper which have low expansivity, to choice a reasonable papermaking conditions-freeness of pulp, density of sheets and drying tension etc.-connecting with other physicalproperties.

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