Sorption and thermochemical heat storage attracted considerable attention recently because it offers various opportunities in the design of renewable and sustainable energy systems. Heat and mass transfer remains currently the main limitations whose overcoming would facilitate their introduction to the market, a step which has been pointed out as long overdue. In this paper, main aspects regarding the heat and mass transfer in solid sorption heat transformers, seen purely from the perspective of the size of particles and the thickness of sorbent layers, are reviewed for both open and closed units. Because mass and heat transfer challenges are common problematic in adsorption, chemical heat pumps and chillers as well as in thermochemical energy storage, relevant data from related literatures will be considered. This work has been limited to pulverised or pelletised beds. One trend is towards the use of relatively small grain size adsorbents in physical closed adsorption heat transformers. The authors expect to provide valuable starting points for designers of sorption or thermochemical energy storage units. (C) 2014 Elsevier Ltd. All rights reserved.