Laboratory drying experiments were done with a standard tensile testing device to study basic mechanisms of moisture induced tension variation. Also, pilot machine experiments were done to compare with the laboratory tests. The results show that the tension variation of paper is generated by a combined effect of moisture variation and straining during drying. The laboratory experiments indicate that tension variation is induced by strain differences in paper web. Tensile stiffness, which is affected most by wet straining, is almost constant between areas of different initial moisture contents. On the other hand, pilot tests showed only small effect of the initial moisture variation. In rewet experiments it is found that dried-in strain is recovered when paper is rewetted.