Besides having positive impact on sustainable development, natural building materials also have technical properties comparable with standard materials and important additional qualities. This article focuses on thermal, moisture and biological properties of thermal insulating materials based on vegetal and animal fibres.There is a lack of data regarding natural building materials and furthermore the properties of these types of materials can be site-dependent. Therefore the natural insulating materials have been tested for thermal, moisture and biological properties. In the research array, there were following materials: treated sheep wool, raw sheep wool, wood fibre, hemp, flax, straw bale and compressed straw panel. The main examined parameters are the thermal capacity, thermal conductivity, volume density and sorption isotherm, which are stated and compared. In addition to that, the microbiological identification tests were made together with the mould growth observation.The results of all tests and measurements are stated and discussed in the article with the emphasis on the situation in the real building stock where the test bordering conditions possibly occur