Used some cheap emergency (space) blankets as solar reflective window film.
(Heath Robinson would have been proud of me😏).
Of course nothing beats mooring in the shade of a large tree, so this is for when that option is not available and for when under way.
I proved the concept worked well last summer at home, so I’ve temporarily lined our boats windows with this same cheap as chips film.
Bramble - 10 Large Multi-Purpose Insulated Foil Emergency Blankets - 210x160cm for £9.99 from Amazon (sorry - other suppliers are available😏).
On the plus side the perceived reduction in heat is quite noticeable.
There are a few downsides though…
On dull days the effect is akin to wearing dark glasses inside, so rather gloomy.
Also it is a bit of a faff cutting to size and temporally attaching to each window with masking tape.
At home I’ve treated each of the south facing bedrooms and cut separate panels for the opening windows. However, on the boat we normally remove the hopper glass for ventilation, so only about 2/3 of each window has been treated. The effect will obviously be less, but I feel it’s still been worth the effort.
A single pack was more than enough for the boat + selected windows at home.
I’ve no idea how big any compromise is by using my cheap method compared with purpose made solar film, but it works well enough for me for some temporary relief during this heatwave.
Incidentally, the fold lines make it easier to cut the panels square.