Posters have many obvious enemies: light, dirt, insects, mold, greasy fingers, coffee, fire, thumbtacks, tape, careless handling, water and high humidity. Some of these hazards that threaten your valuable collection can be averted by using a little common sense: don't smoke or drink while handling unprotected posters; wash your hands before handling them; don't leave your posters on the floor where your two year old or your pets can get hold of them.
...But, there are a host of other hazards that may never have occured to you:
* damage from contact with improper storage materials and framing
* damage from contact with other posters
* damage from fluorescent light exposure (most fluorescent light sources are every bit as damaging as exposure to direct sunlight)
* ...and perhaps the scariest of all is damage from materials you may have been sold as being "archival" and/or "acid free". (There are no government standards for the term "archival" and many retailers and manufacturers use the term very loosely.)
The first question to ask yourself is "What do I want to do with my posters?".
If your primary objective is to display your collection, framing is the most obvious solution. In that case, your first priority is to find a quality framer who is thoroughly familiar with archival materials and framing techniques. If a framer does not know what "archival" means, find another one.
At a very minimum you need to make sure that any matte board and backing board used are acid free. If you do not want to use a matte, it is best to select a high profile moulding that can accomodate a "spacer" to keep the glass from coming into contact with your poster. (The problem with glass coming into contact with a poster is that humidity can become trapped between the two surfaces. If this happens, the poster can become wet and adhere to the surface of the glass.) The other problem with glass is that it can break and puncture the suface of a poster. Plexiglass solves that problem. Plexiglass also comes in an ultra-violet filtering variety which can help solve fading problems for very little added expense. (Framer's Workshop in Berkeley can help you you with your framing needs - they ship too.)
But what if you have too many posters to frame or if framing everything is beyond your means?...Then it's time for you to take a serious look at Mylar Poster Sleeves.