plastic is the answer
http://www.enotes.com/how-products-encyclopedia/raincoat
Charles Macintosh is credited with inventing waterproof fabric. He would later use this fabric make a raincoat still know are the Mackintosh.
When rain hits a raincoat, the outer fabric repels the water and prevents it from soaking through to the wearer. The water forms droplets on the surface of the raincoat and eventually runs off. This helps keep the person wearing the raincoat dry.
A raincoat is impermeable because it is made with fabric or plastic that is made to repel water.
Nylon can make the raincoat because it has elastic, have a low moisture regain, exceptionally strong and soft.
A raincoat is made from waterproof or water-resistant materials that prevent water from penetrating through the fabric. The design often includes features like sealed seams and adjustable closures to keep moisture out. This barrier allows you to stay dry even when exposed to rain. Additionally, the fit and coverage of the raincoat help to shield your body from raindrops.
Plastic is easy to mould into garments, and is waterproof.
a raincoat
Charles Macintosh worked as a Scottish chemist and inventor in Glasgow, Scotland. He did not attend a university, but instead gained his knowledge through practical experience and experimentation. He is best known for inventing the waterproof fabric that bears his name, the Mackintosh raincoat.
One compound word you can make is "raincoat."
Most raincoats are made from nylon. Some raincoats today are still made with cotton or wool fabric which has been treated with a water repellent.
Ramie is a strong fabric that is blended with cotton, nylon and other fabrics.