'Tents are coated with a thin layer of aluminium hydroxide.'' Why ?

Explanation

Tents and umbrells cloths are made of tightly-woven fabric so that water with its high surface tension cannot easily penetrate. But falling raindrops can overcome that surface tension and wet the fabric which will then start seeping water to its other side. Aluminium hydroxide is water insoluble and water repellent. Thus, it drains off the raindrops before they can wet the fabric. Hence, tents are coated with a thin layer of aluminium hydroxide.