Still, it’s one of those easy safety habits that costs practically nothing.
If moving a bottle out of direct sunlight takes a few seconds, why not do it?
Why Can a Water Bottle Be a Fire Risk?
The explanation comes down to a little bit of optics.
A clear bottle filled with water can bend incoming light. Because the bottle is curved, the water and bottle can sometimes redirect sunlight toward a smaller area.
Think about what happens with a magnifying glass.
Sunlight passing through the glass can be focused onto a tiny spot. That spot can become considerably warmer than the surrounding area.
A water-filled bottle isn’t necessarily going to behave like a perfectly designed magnifying glass, but the basic optical principle is similar.
