Stretch (elongation) is defined as the ability of the fiber network to elongate under load without breaking, and is a good measure of the toughness of paper. It is determined by fiber elongation, and the distortion of the fibrous network. It is measured as a part of the tensile strength test, being defined as the strain of the paper at breaking point [13]. Fig. 1c shows the stretch of sheets produced with and without CNFs in extracted and un-extracted conditions, respectively. In the beaten case, the results demonstrate that the stretch values of extracted samples at breaking point were less than the control, however, with increase in the concentration of CNFs, stretch was improved. For instance at 10 wt% CNFs for beaten samples, the increase in stretch values were 48% and 27% more than the unextracted and extracted sheets without CNFs, respectively (Fig. 1c). Similar stretch behavior took place in the unbeaten condition. As mentioned earlier, the reason for this phenomenon is attributed to the differences originating from the chemical nature.