The term thermal envelope refers to the heat control layer of a building, the insulation, the most critical building element in achieving passive house standard. The thick insulation barrier (yellow) of the passive house essentially forms the thermal envelope in tandem with the airtight membrane system (red). The insulation must be a continuous blanket layer, free from any breaks or gaps. Any point in a building where there is a break in the run of insulation is called a thermal bridge, also commonly known as a cold bridge. The insulation barrier must completely encapsulate the structure, ensuring there is no thermal/cold bridging.