The present invention relates to orthopedic casts. In particular, some implementations relate to a cast system having one or more underlayment components that are disposed between an internal surface of a cast or splint and a body part that is covered by the cast or splint. While the underlayment components can include any suitable element, in some cases, they include a compression sock and a padding layer. Additionally, in some such cases, the compression sock and the padding layer are capable of moving (at least somewhat) with respect to each other such that shearing movement between the skin of a casted appendage and the cast itself is configured to take place between the padding layer and the compression sock (and/or another portion of the underlayment). Additionally, in some cases, one or more components of the underlayment comprise an antimicrobial material, such as a bamboo fabric. Other implementations are also described.