The story is often told of Napoleon's men freezing in the bitter Russian Winter, their clothes falling apart as tin pest ate the buttons. This appears to be an urban legend, as there is no evidence of any failing buttons, and thus they cannot have been a contributing factor in the failure of the invasion. Uniform buttons of that era were generally bone for enlisted, and brass for officers. Critics of the theory point out that any tin that might have been used would have been quite impure, and thus more tolerant of low temperatures. Laboratory tests of the time required for unalloyed tin to develop significant tin pest damage at lowered temperatures is about 18 months, which is more than twice the length of the invasion. Nevertheless, some of the regiments in the campaign did have tin buttons and the temperature reached sufficiently low values (below −40 °C or °F). In the event, none of the many survivors' tales mention problems with buttons and it has been suggested that the legend is an amalgamation of a case of disintegrating "Russian" tin buttons in an army warehouse in the 1860s and the desperate state of Napoleon's army, having turned soldiers into ragged beggars.