Answer: This is a very good question. We will try to give you a short answer while we prepare a long answer by creating a video in our Bubble Talk and a post.
As we have briefly shared on the home page, in order to appreciate the beauty of soap liquid bubbles, we have to borrow the real and working model from nature. That is the atmosphere above our heads and over in the sky. Take a quick look at the following picture:
As you can see, the sun represents the heat source (hot, in the form of heat radiation) and the earth stands for the heat sink (cold, with the help of mainly water). Therefore, the atmosphere in the middle plays multiple and critical roles. To name a few, (1) passing most of the sun light; (2) capturing some of the sun’s thermal energy in the red light region; (3) balancing the thermal equilibrium between the heat source and heat sink, etc. In fact, it is mainly the water vapor within the atmosphere that plays these roles.
Now, comes to this one single obvious fact: without any proper insulation, any structure such as clear, closed and single layer covered structure on earth is hot in summer and cold in winter and also warm during the day and cold at night. Don’t believe it? Test it yourself by build a traditional single layered greenhouse.
Why? Because the temperature inside such a greenhouse is determined by the sun. So the greenhouse is warm and hot during the day and cool and cold after sunset. The heat coming in cannot be stored for use at night. No material is fit to play the triple role that the atmosphere acts in real life except for something in between water vapor and liquid: water bubbles.
Therefore, soap liquid bubbles make a tramendous difference in (1) allowing light coming in; (2) absorbing solar thermal energy in red light region; (3) balancing the temperature upsway during the day and downsway at night.
So no filling of liquid bubble foam in a double-layer glazed greenhouse means the worse case for making a greenhouse in the first place. That critical!