There are plenty of modifications and features available for greenhouses, high tunnels, and hoop houses. As the decisions are being made what features are going to have the largest impact per dollar, a double layer inflation system should be considered. The benefits of having a double layer inflated greenhouse that employs the use of an inflation fan are many fold, but as far as cost-benefit ratio the inflation fan and second layer of greenhouse plastic are difficult to beat. In addition to better insulating the greenhouse or high tunnel a double layer system has real structural benefits as it helps absorb strong winds and helps shed some of the snow during snow events. The short video below goes through some of the specific benefits of a double layer inflated greenhouse system.
If you are planning to purchase a structure be sure to ask about the pricing needed to add a second layer of greenhouse plastic and an inflation fan. If you are planning to fabricate / DIY your own structure it is still worth considering a double layer set-up.
Although many people use two layers of 6 mil UVA Clear plastic an Anti-Drip IRAD greenhouse plastic should be considered for the bottom / interior layer. As a guide for what plastics and products would be needed as a part of a simple double layer set-up check out the links below:
Jumper Hose (helps move air from one half of the tunnel to the other for peaked structures)