An undercast padding, also known as cast padding, is a soft and comfortable bandage that is used underneath an orthopedic cast. Its primary purpose is to provide extra cushioning and comfort for the wearer. Typically composed of cotton undercast padding, it serves to protect the skin from potential irritation and pressure caused by the cast. The padding can be placed either between the skin and cast padding or directly on the skin, depending on the level of comfort required. 

This soft bandage is a crucial component of the casting process as it helps to alleviate the discomfort associated with wearing a cast. Moreover, it assists in preventing skin irritation and pressure sores that may occur during extended periods of wear.