Not all polyethylene foam is made equally. It is safest to use a branded product like Cellu-cushion or Ethafoam from Sealed Air. These are white foams, extruded with clean air. Some polyethylene foams are manufactured with unfiltered air, which introduces impurities to the product. Impure polyethylene foam will yellow and/or become brittle and crumbly. It can take years for this to happen. (I know this from experience! The great deal we got on foam 20 years ago has come back to haunt us)
Keep an eye on they polyethylene foam you have sourced to make sure it is not changing its properties as it ages.
Use barrier materials like acid free tissue, Tyvek, or washed unbleached cotton muslin between foam and objects if you are concerned.
It's best to avoid all colored polyethylene foam, with the exception of black plastazote foam, a form of cross-linked, closed cell polyethylene foam. The most common brand in the US is Volara. It also comes in white.
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Rebecca Newberry
Conservator
Science Museum of Minnesota
Saint Paul MN
(651) 265-9841
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Original Message:
Sent: 03-06-2019 02:27
From: Karen Pauli
Subject: Polyethylene foam
I am a volunteer historian with my local Girl Scout council. Needless to say, we have little to no budget, so I try to find out what are the big box store equivalents to the items we could get from an archival supply business. I work with the old uniforms. Most of the uniform hats are fabric with very little stiffening. To make hat forms to display them on I had bought polyurethane foam at a fabric store and carved it into the various shapes needed. Later, I had heard somewhere that that polyurethane was not "archivally stable"; it deteriorated and disintegrated. National Park Service Conserve-o-gram on plastics showed me that polyethylene foam was more stable and safer for the hats. I scrounged packing forms and cut those apart and glued them into blocks I could carve into hat forms. Later I found a company on Ebay that was selling slabs of polyethylene that worked even better. It seemed to come in two colors, white and grey. The Conserve-o-gram warned against using the anti-static pink foam; I assumed that was because the chemicals that made it anti-static would be detrimental to the artifacts. I found more forms of polyethylene and more uses for it. Old troop flags must be kept on their flagpoles says the Council, so I have been using foam pipe insulation to put around the wooden pole to separate it from the flag and protect the flag from further staining from contact with the wood. Pool noodles are polyethylene and are usefull for other things. For example, arms inside of dress sleeves.
My question is: Are there types of Polyethylene (other than the pink) that I should not be using? Are the pool noodles safe, or is the dye that makes them different colors going to harm the artifacts? Are the white and grey the natural colors of the foam? Does the white foam have some sort of bleaching agent to make it white that I should beware of? In everything I've read, every webinar I've seen, nothing has been said or even implied that there are good and bad types of polyethylene. Can you please clarify?