In a polymer nanocomposite, since the reinforcing particle is at the nanometer scale, it is actually a minor component in terms of total weight or volume percent in the final material. If the nanoparticle is fully dispersed in the polymer matrix, the bulk polymer also becomes a minor, and in some cases, a non-existent part of the final material. With the nanofiller homogenously dispersed in the polymer matrix, the entire polymer becomes an interfacial polymer, and the properties of the material begin to change. Changes in properties of the interfacial polymer become magnified in the final material, and great improvements in properties are seen. Therefore, a polymer nanocomposite is a composite where filler and bulk polymer are minor components, and the interfacial polymer is the component that dictates material properties. The most common use of polymer-clay nanocomposites has been in mechanical reinforcement of thermoplastics, especially polyamide-6 and polypropylene. The polyamide-6 clay nanocomposite produced by Ube/Toyota was used to replace a metal component near the engine block that yielded some weight savings. The clay in this application improved the heat distortion temperature of the material, allowing it to be used in higher temperature applications. GM/Blackhawk has also announced polypropylene-clay nanocomposites for automotive applications, and the clay brought an increase in flexural/tensile modulus while maintaining impact performance.

The use of polymer-clay nanocomposites for flame retardant applications is becoming more common, especially as it is realized that the clay nanocomposite can replace part of the flame retardant package while maintaining fire safety ratings at a lower flame retardant loading. This results in a better balance of properties for the nanocomposite material compared to the non-nanocomposite flame retardant product, and in some cases, better cost for the flame retardant resin, especially if the organoclay is cheaper than the flame retardant which it replaces. It should be noted that the organoclay can replace traditional flame retardant on more than a 1:1 by weight basis, meaning 1 g of organoclay can replace more than 1 g of traditional flame retardant, resulting in a lighter material. In fact, it appears that clay nanocomposite systems serve as a nearly universal synergist for flame retardant additives, with some exceptions.

Another common application of clay nanocomposites is for gas-barrier materials. Clay nanoparticles create a complex network in the polymer matrix, such that various gases either diffuse very slowly or not at all through polymer chains and pinholes in thin films or thicker polymer parts. The success of clay nanocomposites to impart decreased diffusivity of oxygen and water has led to their use in food/liquid packaging to keep foods fresher longer.