Nonwovens made of poly(ethylene terephthalate) (PET) and ethylene-vinyl alcohol copolymer (EVOH) are found to become highly fire resistant by treating with amorphous sodium polyborate (SPB). The fire-resistant nonwovens with 10-mm thickness show a gradual temperature increase up to 127 A degrees C and no hole, when their back sides are fired with a gas burner for 12 min. The analysis using the EPMA and the DTA/TG indicates that the SPB foam promotes the formation of char (carbon) layer, and that the char layer together with the SPB foam insulates inside from the oxygen and the heat.