A polytunnel is a tunnel made of polyethylene, usually semi-circular, square or elongated in shape. What it does is that it uses the solar radiation from the sun warming the plants, soil and other things inside the tunnel faster than heat can escape the structure.
Polytunnels are usually used to increase the humidity and heat of an area where it is not available. The tunnel itself can protect crops from intense heat and other severe types of weather in your area. This will allow off season crops to be grown without any problem.
It basically is a controlled environment where you can grow any type of plants that you wish to grow. A greenhouse if you prefer calling it that. This is perfect for areas that have extreme weather conditions. In the video, they will show you how you can make or set up your own polytunnel.
Although they purchased all the materials but the process and everything is the same.