The thermal and flammability properties of nylon 6 nanocomposites, based on Na+-Laponite(r) (LP) and Na+-Montmorillonite (MMT) nanoparticles were investigated. Nylon 6/LP (5 wt%), nylon 6/MMT (5 wt%), and nylon 6/LP/MMT (2.5 / 2.5 wt%) nano-composites were prepared using a hydrolytic in-situ polymerization technique. Having 2- to 7-fold difference in particle aspect ratios and 0.5-fold difference in particle surface charges, LP and MMT nanoparticles produced 45 and 51 % reduction in peak heat release rate (peak HRR) of nylon 6, respectively. LP and MMT nanoparticles were both very effective...