PET nonwoven is classified as flammable material (LOI 21%). Because of using PET nonwoven by thermal isolation of various types of rooms (attic, loft and other) the requirement of fire safety is very high. One of the possibilities to receive higher flame retardant is impregnation of PET nonwoven. The purpose of this work was to compose a formula of impregnation bath. The PET nonwoven made from recycling materials (PET bottles) was used for the research. The impregnation bath was prepared in the form of a mixture of two commercial products: aqueous solution of sodium silicate – sodium water-glass R-145 and styrene acrylic aqueous dispersion – Triostat TO. After the impregnation process thermal tests (DSC, TGA) and microscopic investigations (SEM) of PET nonwovens were performed. The flame retardant effect was described by Limited Oxygen Index-LOI. By treating of PET nonwoven satisfactory and acceptable technically flame retardant effect was received (LOI ca. 28%).