The last form of insulation is vacuum insulation. Vacuum insulation- “a form of thermal insulation consisting of a gas-tight enclosure surrounding a rigid core, from which the air has been evacuated”. It is very effective because it eliminates the transfer of heat in conduction and convection. In conduction, molecules travel between air, but by removing the air and creating a vacuum, kinetic energy cannot be transferred and conduction cannot happen. A convection is created by the movement of molecules from one location to another, but in a vacuum, there are so few molecules that a convection current cannot be produced. Vacuum insulation has an R-value of 25 per inch, making it a much better insulator compared to conventional materials. While it is a great insulator, it is also susceptible to puncturing. Once punctured, its insulating abilities will be reduced. Also, they are expensive and impractical for many buildings. A 30 x 35 panel can cost $345 and a 60 x 75 panel can cost $600. This makes them difficult to access for many. Theoretically, the best solution would be to start with an insulating concrete form and to insulate the walls with a vacuum insulator because this has the highest R-value. This house would have an R-value of 45, which means it is considered a passive house. However, this combination can be relatively expensive, especially with the vacuum insulator. The vacuum insulator has a higher risk to puncture and diminish its insulating effects. A more reasonable option would be to have an insulation concrete form and insulate the walls with foam board. Since foam board has a low R-value, lots of material would be needed to make up for heat loss. The walls could be very thick because of all the insulation needed. This could also add more costs since more material is needed. For the foam board, the extruded polystyrene foam would be the best option. It has a good balance between performance and price and is also easily accessible. Expanded polystyrene foam has a low R-value and would not be the best option. Polyisocyanurate insulation is not the best option as well. Other than its expensive cost, this type of foam uses chlorofluorocarbons, which destroy the ozone. The purpose of the passive house is to combat climate change by living in a house with zero carbon emissions. It would not be logical to live in a house combating climate change, while its insulation is adding to the hole in the ozone layer. This ultimately could cause a positive feedback loop and make the situation worse. To conclude, there are many different factors determining which insulation to install.