Long Johns are a type of thermal underwear designed to keep the body warm in cold weather. They typically consist of a long-sleeved top and long pants, made from materials like cotton or polyester. Long Johns are often worn as a base layer under regular clothing, providing insulation without adding bulk. These garments are popular among outdoor enthusiasts, such as hikers and skiers, who need extra warmth during their activities. Long Johns can also be worn for everyday comfort during winter months, making them a staple in many people's wardrobes when temperatures drop.