For centuries, lambs wool has been the traditional choice for keeping warm at sea. Mainly this is because wool retains body heat... even if it gets wet! This unique feature is unmatched by modern synthetic materials, and so that's why we still recommend it for blankets, sweaters and watchcaps.
Wool also tends to assist the body in regulating its own comfort level across a wide range of temperatures and sailing conditions, thereby making it ideal for layering. For example, in most locations a mid-weight wool blanket will be comfortable for year round use, but for extreme cold it might be necessary to add a second blanket or bedspread.
Wool is also naturally fire-retardant, without added chemicals or synthetic irritants. This makes it suitable for emergency use aboard the ship, such as first-response trauma care, or even snuffing out flames.