105
Made a very high tech saddle sun cover
(sopuli.xyz)
My bike is exposed to the sun on the balcony where I keep it. This is probably not so great for the leather saddle, so I improvised a sun cover from some wire and folio. This highly advanced design doesn't trap heat underneath.
I suggest a cardboard box
That would be reasonable as well.
But why stop there!? You could improve the thermal properties by covering it with reflective folio and adding holes for ventilation! Or you could skip the holes and have pretty good water resistance as well.