A supercritical CO2 (scCO(2)) foaming technology was used to develop a PLA foam with a thermal conductivity as low as 30 mW/m-K. The PLA foam's larger optimal expansion ratio and strong infrared (IR) block ability greatly helped to achieve this outcome. Unlike the PS foams, in which nonbiodegradable carbon particles are often added to block the IR thermal radiation, the PLA foams' intrinsic IR-absorbing characteristic, which acted via the ester group in the PLA molecular chain, further enhanced its environmental impact. Overall, environmentally friendly PLA foams, made by using the nontoxic scCO(2) foaming method, offer a sound alternative to PS foams.