This study focuses on the hardness and surface texture of the rubber, sponge, notched and ribbed projectiles and their performance to clean tubular heat exchangers when the injection rate was varied from 1 inj./5 min to 1 inj./10 min. Fouling and visualization experiments were conducted in which CaSO4 solution was used as foulant. The fouling experiments were performed to compare the cleaning ability of the different types of projectiles, while the visualization experiments were aimed at determining what caused the cleaning action of the projectiles. Injecting the projectile once every 5 and 10 min changed the propensity of the fouling resistance from a linearly increasing, as in the case of no injection to an exponentially decaying growth. The notched projectile had the best cleaning capability, while the smooth rubber projectile the least. The asymptotic fouling resistance for the notched projectile was 3 times less than that of the smooth rubber one in case of 1 inj./10 min, and 4 times less for 1 inj./5 min. For a better cleaning, the outer structure of the projectile should be made from a material that is stiff and rough in order to remove the fouling layer. It should also be flexible in motion such that it allows the brush mechanism to take place, i.e. compression of the projectile along the tube surface followed by its release then finally cleaning of the tube surface. (C) 2014 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.