Cottonclads were a classification of steam-powered warships where a wooden ship was protected from enemy fire by bales of cotton lining its sides. This provided some protection from enemy fire, but not to the extent of ironclads. Cotton-clads were prevalent during the American Civil War, particularly in the Confederate States Navy for riverine service.
The heavy bales of cotton slowed small arms fire, but at times the cotton would catch fire from artillery shells.
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The original article can be found at Cottonclad warship and the edit history here.