Choice of building materials today is influenced by numerous factors. One of the important factor except to good physical and mechanical properties is also the environmental impact. Just the organic processed of fibreboard is significantly different from other commonly used thermal insulation materials. In addition to good features the fibreboard has also in terms of fire protection poor quality and that it is a combustible material. It is for this reason that we have decided to make a fire test of fibreboard. As the test method, we chose a weight loss in the heat sources, and by delaying the time depending on the heat sources and the type of fibreboard. The theoretical part of the paper deals with the description of the material examined and the test methodology. The practical part consists of evaluation testing. Samples tested were two types of fibreboard, which is mainly used as thermal insulation material floating floors. The first test material is a fibreboard produced by pressing wood chips in a single layer. The other test materials consisted of pressed fibreboard in the form of thinner plates and then glued of several layers into a single unit. In addition to tracking the speed of weight loss, depending on the density of the samples we were compared and depending on the duration of action of flame and rate of weight loss of the sample.