Polyethylene bags

Here's a query for Conservation DistList members.  And I apologize in
advance if this problem is too elementary for many readers.  I'm not a
conservator, and don't have ready access to current literature on this
topic.

The 1990/91 archival materials catalog for University Products, Inc.
(P.O. Box 101, 517 Main St., Holyoke, MA 01041) advertises on page 26:

"NEW Archival Quality Polyethylene Bags. . .[made of] 2 mil uncoated
polyethylene, which is chemically inert and will not harm your valuable
materials."

The cost for these polyethylene bags is *considerably* less than for
those made of Mylar D, which is what we've been using to store
pamphlets, comic books, pulp magazines, etc., which are then encased in
acid-neutral boxes.

I've been given conflicting advice on the use of polyethylene for
long-term archival storage.  Can a Cons. DistList reader offer some
advice?  Spend the $$ and stay with Mylar (polyester)? OK to switch to
polyethylene?  Other?

Thanks!

Brenda McCallum,
Head Librarian,
Popular Culture Library,
Bowling Green (Ohio) State University

                                  ***
                  Conservation DistList Instance 4:50
                  Distributed: Sunday, March 24, 1991
                        Message Id: cdl-4-50-005
                                  ***