AbstractFor the mechanical properties of paper, tensile testing has been widely used. Among the tensile properties, the tensile stiffness has been used to determine the softness of low-density paper. The lower tensile stiffness, the greater softness of paper. Because the elastic region may not be clearly defined in a load-elongation curve, it is suggested to use the tensile modulus which is defined as the slope between the two points in the curve. The two points which provide the best correlation with subjective softness evaluation should be selected. Low-density paper has a much lower tensile strength, but much larger elongation at the break. It undergoes a continuous structural change during mechanical testing. The degree of the structural change should depend on tensile conditions such as the sample size, the gauge length, and the rate of elongation. For low-density paper, the tensile modulus and the tensile strength should be independent of each other. The structure efficiency factor (SEF) is defined as a ratio of the tensile strength to the tensile modulus and it may be used a guideline in developing superior low-density paper products.