In this study, insulation material was developed using polylactic acid (PLA), which is one of the most widely-used biodegradable polymers. The PLA was fabricated into a fiber mat shape using the electrospinning method, and NaCl salt was added to achieve thinner fiber diameter. This fiber-based mat showed lower thermal conductivity than PLA blocks but had poor tensile strength and heat stability. To improve these mechanical and thermal properties, ammonium polyphosphate (APP) and acrylic acid (AA) were added; AA was used to better bond the APP with the polymer matrix. The APP/AA mixed PLA fiber mat showed improved performance overall; with the addition of these materials, the thermal conductivity was about 35 mW/mK, which was slightly lower than before, the tensile stress improved about two times. Thermal stability was also augmented as the increase in the weight percentage of the sample residue after the thermogravimetric analysis indicated.