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4mm twinwall polycarbonate is the best choice, for reasons which I'll explain. Where you live in Edinburgh, Scotland, the days are shorter and the light less bright - 4mm twinwall polycarbonate allows 80-84% light through, compared to single wall polycarbonate, which allows 94-96% (note that 3mm glass allows 97-98% light). This might sound like a big ...

Just like double paned, insulated glass, different thicknesses provide different R-Values. Manufacturers/retails will sometimes list the R-value for their products. Here you can find some R-Values for twinwall. The greater the thickness, the more effective it is as an insulator. Determining which thickness to get will be based on your climate, what you plan ...

I have a univent and left it in the garage over the winter and had to replace the cylinder. Something happens to the gel when it freezes

Cold frames and cloche type arrangements are not the same thing. I'd leave the cloche ones clear, probably make the whole thing out of twin polycarbonate. It has insulating properties of its own anyway, and although you think no light will get to the plants because of the fence, that isn't always true. For instance, if the fence were white, or a pale colour, ...

A clear film will transmit the most amount of light. Blue and green coloured plastics will transmit a lot of the light in the blue to blue-green wavelengths, but cut out much of the light in the red wavelengths. From the diagram above looking at PAR, it can be seen that red light is the most efficient waveband for plant growth. A blue plastic is likely to ...

One thing you left out of your question is where the heat is coming from. Understanding this might help you come up with a better design. Please bear with me. A cold frame extends the growing season by keeping the local environment within the cold frame more comfortable for the plants than the colder outside environment. To retain heat, there has to be a ...

Cold frames work very well with one giant caution; They will get to very high temperature very fast when the sun hits them ( real greenhouse effect). I built one in zone 5 with a home-made operator to open it depending on the temperature. My design was not reliable over time so I just opened it every morning which was not very good. Today I expect there are ...

Your link points to images which show mostly the upright type of cold frame; I have no experience with these but do have some experience with the flat horizontal type, so take my comments with this in mind. I guess the upright type reflects the fact that gardens are a lot smaller than they used to be. Frames are great protection against wind, can improve ...

It seems to me 4 mm and 6 mm sheets are mostly not very sturdy? You need quite some framing to get it halfway stable and even then they can be destroyed quickly. Most 10 mm sheets are stable enough, isolate a bit and let enough light through? So they seems for many places the best choice. I am myself working on such a solution, but using wood for framing, ...