Hi, I'm doing a group investigation on external wall insulation for my school building. The walls do not have a cavity and thus it has been proposed to put insulation over the exterior render of the wall. This is a fairly common building procedure. However, my task is to investigate the plausibility of using recycled materials as insulation and once I have decided what to use, I will need to calculate the thermal conductivity. My proposal is to use a mixture of supermarket plastic bags and other mixed recycled packing plastics, stuffed between the exterior of the existing wall and a new exterior wooden cladding. With only standard school equipment, how could I measure the thermal conductivity of my custom insulation in order to numerically compare it with existing insulations?