How much do nanoparticle fillers improve the modulus and strength of polymer foams?

Nanofiller reinforcing agents can significantly improve the strength and modulus of polymer foams. But these improvements are often accompanied by changes in foam density (or equivalently the expansion ratio or void volume). The efficacy of nanofillers as reinforcing agents can only be judged once the density differences are accounted for. We review the literature and show that representing the data on Ashby charts of modulus against foam density is an effective way of evaluating whether nanofillers have a significant reinforcing effect or not. The literature suggests that strength and improvements due to nanofiller - after accounting for foam density changes - are typically modest for thermoplastic foams. However, major improvements are possible for reactively generated foams, especially flexible polyurethane foams.