Body armour was only worn by the heavy cavalry of the rival nations in the Napoleonic wars and then not by all nations or all units. The basic infantryman was too encumbered to wear armour and often made do with his blanket roll tied diagonally across his chest to offer some protection and a simple hat, which offered very limited protection against a sword cut from above. The use of blanket rolls and cloaks to do this was common among the French, Prussian and Russian armies but not often seen among the British. The only relic of medieval armour was the cuirass, a solid body plate often but not always with front and back plates. The cuirass was proof only against sabre or bayonet and not effective against muskets or artillery so was abandoned in many armies. It was heavy and an unhorsed trooper could have difficulty getting up, as Lord Wellington put it they “struggle like a Turtle”.
The French heavy cavalry were famous for their Cuirassiers and questions of effectiveness aside they would have been an impressive sight. The Austrian and Russian armies also fielded such troops although the Russians at times dropped the usage of armour only to later reintroduce it. The British cavalry did not use armour during this period. This was probably due to the fact that the heavy armour required big heavy horses to carry and the British cavalry were short of good horses throughout this period. The Austrians favoured just a front breastplate to save weight but in a confused melee this left the back vulnerable and engagements against French heavy cavalry bare this out as the Austrians suffered 13 casualties to every 8 the French suffered. Armour during this period saw very little if any technological development.