Visually, very little, internally as well as externally. Structurally, the inner leaf of the wall is built from timber panels. Once first fix plumbing and electrics are completed the panels are filled with insulation (typically glass wool) and then 'closed off' with plasterboard. On the outside of the timber frame panel a block wall is typically constructed which is then harled (other external finishes occasionally specified include natural stone, brick or timber cladding). An air cavity is maintained between the external cladding and the timber frame.