Why put material in doorways?

Hi, I have been plagued by a question that I cannot seem to find the answer to.

I am wondering why the Japanese people have those little material flaps inside their doorways and outside of some restaurants? You see it often enough in movies and in anime.

I have looked everywhere else and cannot find an answer, let alone what they call them.

Can anyone help me? I would be really appreciative if someone could put my mind at rest.

Thanks x

Noren (ﾅｯｺ・ are traditional Japanese fabric dividers, hung between rooms, on walls, in doorways, or in windows. They usually have one or more vertical slits cut from the bottom to nearly the top of the fabric, allowing for easier passage or viewing. Noren are rectangular and come in many different materials, sizes, colors, and patterns.

Noren are traditionally used by shops and restaurants as a means of protection from sun, wind, and dust, and for advertising space.[citation needed] Sentｨｭ (commercial bathhouses) also place noren across their entrances, typically blue in color for men and red for women with the kanji 忰 (yu, lit. hot water) or the corresponding hiragana ､・
from Wikipedia :P

http://en.wikipedia.org/wiki/Noren

Noren are traditionally used by shops and restaurants as a means of protection from sun, wind, and dust, and for advertising space.

Thank you so much Kribeli!! You have been most helpful. I am glad that I can finally put this question to rest.

Have a good night.