Coal fly ash is primarily by-product produced during combustion of coal in power plant. Fly ash is obtained by electrostatic or mechanical methods during separation of fly ash particles from the flue gas. The article presents the characteristics of two types of fly ash: fluidized and conventional. The results of the chemical composition analysis, particle size distribution, structure of fly ash and characteristic ash fusion temperatures are presented. The results of thermogravimetric analysis (TGA) of the ashes were also presented. Fly ash recycling methods are discussed. In particular, methods of using fly ash as a filler in the production of rigid polyurethane foams were presented. The paper also presents environmental aspects of the fly ash application in polyurethane technology. The Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) was used for the qualitative and quantitative analysis of the elements in the fly ashes. The ash melting points were performed using the microscopic - photographic method in accordance with the PN-ISO 540: 2001 standard. The tests were carried out in a reducing and oxidizing atmosphere.