Impact strength and tensile energy absorption of polymer-clay nanocomposites were measured using polymers that are glassy or rubbery at ambient temperatures. The results highlight the apparent contradictions that arise in these tests. Polystyrene, with initially low toughness, suffered a decrease in impact strength of 3% (notched) and 23% (un-notched) but the tensile energy at break increased by 120%. ABS suffered a catastrophic collapse of toughness in all three tests of up to 90%. A suggestion is that the arrangement of comparatively rigid mineral tactoids inhibits the toughening function of the rubbery zones. The use of poly(epsilon-caprolactone) showed that processing-induced degradation of surfactant did not significantly impair toughness. There is an emerging view that clay reinforcement is more effective with polymers above T-g but these results suggest that the interpretation of impact strength, a property highly rated by industrial users, is less easily explained. (C) 2008 Elsevier Ltd. All rights reserved.