While the ubiquitous PET bottles used for water or pop often get a bad rap, the used bottles are being upcycled in poorer parts of the world as part of roofs. I have two recent examples which are very different. The first uses the bottles as an internal light source. The bottles are filled with water (a touch of bleach to prevent microbial growth) and then placed in a hole cut into the metal roofing material. After being sealed into place, sunlight is collected by the upper part of the bottle and diffracted throughout the living quarters below providing the same light as a 40- to 60-watt incandescent bulb.
A more recent invention also upcycling PET bottles involves cutting the bottles into strips and ultrasonically wleding them to create a thatch roof alternative.