"twin wall polycarbonate sheet off next doors conservatory. "
I have 4 sheets of this, and have set them up over some seedlings as a sort of ridged tent with ends blocked by glass.
I am coming to the conclusion that they don't let enough light through, or are possibly even reflective, to stop the conservatory getting too hot. The seedlings look pale and drawn (perfectly good soil, enough water).
Does anyone know if this is true?