Cellular polymers are of great technological interest in sectors such as construction and automotive because of their low thermal conductivity, weight, and cost. Nowadays, modern society needs specific materials for each application. Therefore, it is necessary to produce new and advanced materials as technology evolves. In this framework, a new generation of cellular polymers with enhanced properties was developed during the last decade: the so-called nanocellular polymers. Nanocellular polymers are porous materials characterized by cell sizes below 1 micron. These materials have aroused great attention owing to their very interesting combination of properties. For instance, as a result of their nanometric cell size, these materials present a reduced thermal conductivity of the gas phase due to the Knudsen effect.

There are plenty of theoretical works hypothesizing the thermal insulation performance of nanocellular polymers. However, there is a lack of experimental results, especially at low densities. Thus, in the present work, we aim to study the thermal conductivity of low-density micro-and nanocellular poly(methyl-methacrylate) (PMMA) to evaluate the heat transfer mechanisms acting on these structures. A collection of samples covering densities from 100 to 230 kg/m3 and cell sizes of 400-4000 nm are prepared by gas dissolution foaming. The thermal conductivity is measured using a heat flow meter. The results are analyzed to understand the contribution of each transfer mechanism to the total thermal conductivity. The conclusions of this work allow identifying the real potential of nanocellular polymers and the next challenges to be accomplished to improve their performance.