The polarization catastrophe model also theorizes that, with a high enough density, and thus a low enough molar volume, any solid could become metallic in character. Predicting whether a material will be metallic or insulating can be done by taking the ratio R / V, where R is the molar refractivity, sometimes represented by A, and V is the molar volume. In cases where R / V is less than 1, the material will have non-metallic, or insulating properties, while an R / V value greater than one yields metallic character.