There are a number of items referred to as rain guards. I am assuming that you are referring to the rain guards that are mounted on the outside of a car window. These are also referred to as side window deflectors.
The side window deflector is used to keep rain or wind from coming into the car when the window in open a small amount. People often leave the window partially open to get ventiliation or when then smoke. The rain deflector will allow the air to circulate or the smoke to leave the cabin while keeping rain and wind out of the car.
The side window deflectors are custom designed for each vehicle.
A waterproof raincoat is a shell whose purpose is to block the rain.
Charles Macintosh invented the waterproof coat in 1824
anorak raincoat!
http://www.enotes.com/how-products-encyclopedia/raincoat
Plastic is easy to mould into garments, and is waterproof.
You can't use a property, as it's a description of something a substance does. A better question would be to ask 'What are the properties you would look for in a material to be used for a raincoat?' You'd want it to be waterproof, flexible, hard wearing and comfortable.
winter knits, watch, wrap, wetsuit, waterproof raincoat
raincoat, umbrella, stay inside, waterproof clothings and shoes.
A "waterproof cloak" or "raincoat" in Spanish is "impermeable". It is pronounced "eem-pare-may-AH-blay". Please see this site for confirmation of the translation: http://www.answers.com/library/Translations
Gore-tex
No, raincoats can't be made of silk or wool. The main function of a raincoat is that it is waterproof, so rain slides right off without the person wearing the coat getting wet. Silk and wool are not waterproof.
Charles Macintosh is credited with inventing waterproof fabric. He would later use this fabric make a raincoat still know are the Mackintosh.