The paper presents results of deformation measurements in dry cohesionless sand during free flow in small rectangular model silos using a noninvasive, indirect method called particle image velocimetry (PIV). It is an optical technique for measuring surface deformations from successive digital images. Laboratory model tests were performed with a mass and funnel flow silo to investigate the kinematics of the flowing sand. The measurements were carried out for granular flow in model silos without inserts and in a funnel flow silo equipped with three different types of inserts: cone-in-cone, inverted cone and double cone. The effect of the initial sand density and roughness of silo walls on the volumetric and deviatoric strain in sand was investigated. The accuracy of measurements was discussed. Advantages and disadvantages of PIV were outlined. The results were qualitatively compared with sand displacements obtained with colored sand layers and with the aid of X-rays (initially dense sand). (c) 2006 Elsevier B.V All rights reserved.