Nowadays, cellular polymers find extensive use in a wide variety of applications owing to their versatility and desirable properties. Among these is the heat insulation sector, with an ever-growing demand for enhanced materials that meet the current energy efficiency needs. In recent years, nanocellular polymers, which are defined as cellular polymers with cell sizes below the micron, have become a topic of great interest in the pursuit of materials with the ability to reach lower thermal conductivities. This leap to the nanometric scale leads to the confinement of the gaseous phase into the tiny cells. As the mean free path of air molecules becomes comparable to the cell size, they are more likely to collide with cell walls than with one another, resulting in a reduction of the gaseous thermal conductivity. This phenomenon is known as the Knudsen effect.

However, on top of the challenges involved in producing these advanced materials, the remarkable reduction in thermal conductivity originally expected for nanocellular polymers has proven difficult to achieve in practice. Even though thermal radiation can be neglected for microcellular materials, this mechanism starts to play an important role in heat transfer once the cell size is reduced, which could counteract Knudsen effect. For this reason, new research about this subject should also explore ways to limit the radiation contribution, such as with the use of additives or filler particles as infrared (IR) blocker.

In the present work, micro- and nanocellular composites based on poly(methylmethacrylate) (PMMA) and graphite nanoplatelets (GNP) have been produced for the first time by means of the gas dissolution foaming method, with CO₂ as a physical blowing agent. Materials containing three distinct types of GNP have been characterized, and the influence of these fillers on the resulting cellular structure and thermal conductivity has been studied. These results confirm the IR-blocking behavior of GNP in nanocellular polymers, and show the potential of the proposed approach for further reducing the thermal conductivity of this new family of insulating materials.