Polyethelene plastic is the most desirable for use in storing objects. The polyurethane and other polymers used in plastic bags off-gas and can damage dyes and other aspects in artifacts. You can buy rolls of polyethelene by the pound for about $150 - $175. Using a heat sealer which costs around $35 you can them cut and seal your artifacts for about $0.02 a bag. When you open the bag you can reseal it, leave ventilation holes if you do not have temperature and humidity controls in your collections storage. The polyethelene is porous as are all plastics. The superstition that non-animate, non-lung-possessing objects need to "breathe" or the fear of condensation should not worry if the orginal environment in which the objects were bagged is adequate. The mini-atmosphere held within the bag will not leach through the plastic for about 8 hours. If the environmental controls failed on your collections storage area you would have a window of time to get the machinery back online. If the time extends past that, cut open the bags. We have economically and safely used polyethelene bags in the above described manner for about four years with not one bad incident involving, fine art, natural history, and ethnographic objects of all classes. There have been some who have advised against using plastic with metal but these warnings have not proven to be caused by any measurable evidence. It took me a while to convince others about this system but time has continued to show nothing but good results. The Smithsonian has used this type of bagging for many years. Though there continue to be fears and worries from those who haven't used this storage, I haven't found any real evidence against the preferrability of the polyethelene over other plastics. Paul Apodaca Curator of Native American Art Bowers Museum Santa Ana, CA [log in to unmask] Paul Apodaca [log in to unmask]