820. Canopy Beds and Hats with Brims
If the canopy of a bridal bed is not a handbreadth wide (about 3”), nor is the area three handbreadths below the roof a handbreadth wide, since it was set up before Shabbos, it may be unfolded and re-folded on Shabbos so long as it does not hang more than a handbreadth above the bed. A curtain for closing a window may be used for that purpose even if it is neither attached to nor suspended from the window since it was designed for this purpose.
One is permitted to wear a hat with a brim to provide him with shade. If one spreads out the clothes that he is wearing over his head or in front of his face like a tent and they are both tight around his head and the canopy that he forms is stiff like a roof, then it is prohibited because by doing so he makes a temporary tent.