I mentioned last year about how high the temperatures get in greenhouses even when fully open.

The coolest I can keep mine at, without shading, in summer - and I'm talking fully open here - is 38 degrees. From what people have reported it appears that smaller greenhouses suffer more from excessive heat retention more than the larger ones, persumably because of airflow.

Remember that although some kind of shade curtain inside the greenhouse will diffuse the sun's rays, it will not prevent the heat coming in. You need to put something on the outside - I use green windbreak netting - if possible.

I use Coolglass on the panes I can reach - on the long, south-facing side of the house - it doesn't make a massive difference but every little helps.