Posted: 15/03/2015 at 20:20
I think that there is some confusion here. Those cheap plastic (vinyl) greenhouses are ok, but you are lucky if they last one year and they also leak heat.
Polycarbonate greenhouses are superior to horticultural glass in many ways as they are double glazed, retain heat and do not break. I have a wooden frame greenhouse with polycarbonate glazing and I do not need to screen the glass, I use less to heat and I have had many children's balls hit and bounce off of it with no damage.