During the Crimean War, knitted balaclavas were sent over to the British troops to help protect them from the bitter cold weather. Most of the British troops did not acquire in time the adequate clothing, weatherproof quarters and a good diet. However, according to Richard Rutt in his History of Handknitting, the name "balaclava helmet" did not first appear in print during the Crimean War, but only much later, in 1881.
This type of headgear was also known in the 19th century as an Uhlan cap or aTemplar cap.
In modern American English, when made for those serving in the armed forces, they are usually known as "helmet liners". They are traditionally knitted from wool, and can be rolled up into a hat to cover just the crown of the head, or folded right down as a collar around the neck.
Modern balaclavas can also be made from silk, cotton, polypropylene, neoprene,acrylic or polar fleece.