For the plug flow mode of dense-phase pneumatic conveying, three different types of plugs have been previously defined, and mathematical models for predicting the pressure drop in their pipeline conveying have been established. In literature, the model for plug-I pressure drop is a mechanistic model, which depends on several geometrical and physical properties of materials forming the plug. Thus, the modification of the model with experimentally corrected physical and geometrical material properties has been considered in this paper. The parameters tested experimentally in this study, the plug front angle, void fraction, and bulk density, are the functions of the pressure difference across the plug. Using the new definitions, the plug-I pressure drop model has been modified and compared with the experimental pressure drop obtained for conveying plug-I. It is found that the modified plug-I pressure drop model matches experimental values well within the variation range, from +/- 10% to +/- 30%. All experiments and analyses showed that the main reason that plug-I is enabled is the cohesive force between particles, which are directly linked to flowability. Therefore, the concept of flowability by the Hausner ratio is used to establish the cohesion among plug particles quantitatively by conducting further experiments on a range of materials having Ar from 10(-3) to 10(5). Finally, it is shown that increasing cohesion by wetting the particles enabled the materials to move as plug-I, which would not occur if the particles are dry. (C) 2019 Elsevier B.V. All rights reserved.