In fire design of timber structures the charring rate of the material is a very important property, but the charring rate varies with the conditions in the fire compartment and the characteristics of the wood. Many experiments have been carried out through the years, trying to determine the effect of various properties on the charring rate of wood. This paper gives a summary of the material properties and external factors found in the literature to have the largest influence on the charring rate of exposed wood, i.e. the density, moisture content, chemical composition, grain orientation, permeability, scale effect, thermal exposure, char contraction, char oxidation, oxygen concentration and opening factor, resulting from experiments found in the literature. It has not been possible to determine which properties or factors have the most significant influence on the charring rate of wood, due to large differences between the test conditions and methods, wood species and measurement methods. There is a great need for further testing to determine the relative effect of these properties and factors, and international test methods need to be developed to enable comparison of results from research all over the world. More information about the most important properties and factors can help standardise the calculation of charring of wood, and improve the input to computer models for fire safety design. This will result in more economic fire design of wooden structures, as the calculated residual cross sections will be closer to reality. Copyright © 2010 John Wiley & Sons, Ltd.