Regulating authorities and fire testing laboratories have for a number of years classified materials as combustible or non-combustible. However, many products classified as non-combustible used in building and ship constructions contain small amounts of organic binder, for example phenol and dust binding oils in mineral and glass wools. The binders are often required to achieve the strength of the product. This means that apart from the real non-combustible materials there are a whole range of products which have partial combustible properties. The traditional means of determining whether or not these materials could represent a hazard under severe fire conditions is to subject a sample of the product to 750 °C in a heated cylindrical furnace. Under these thermal conditions the binder in the sample will burn off causing temperature to rise in the furnace. With this background and also with the object of studying the IMCO-procedure in other aspects it was decided at the 23rd session of the IMCO Sub-Committee to perform an interlaboratory test program of non-combustible products for marine use. This report presents the results from that investigation.