For printing paper grades, runnability in the paper machine and in the printing press is partly attributed to the ability of the paper to tolerate flaws and defects in the paper. In these operations the paper fails due to forces applied in the plane of the sheet. It is important for the papermaker to have access to a relevant test method which can characterize those pulp properties applicable to this type of failure. Papermakers knew as early as the 1920’s that the strength of a cracked paper was a unique and useful paper property. This lead to the development of the out-of-plane tear strength test method. The tear test principle has, however, been criticized for many reasons. The most severe criticism lies in the mode in which the paper fails. The mode of fracture in most production and processing operations is seldom an out of-plane tearing, Mode III, but rather an in-plane crack propagation, Mode I.