I agree with Helena’s reply. Don’t know if University products has changed the formula for their glassine but glassine is Not an archival material. While its pH is neutral initially, as it ages it becomes more acidic and brittle. This change can occur over as little as a few months (3-6) or over a longer period, depending on the storage environment If you currently use this material you should also check it periodically with a pH pen. As for the new UP material Helena makes a great point about knowing if it has passed the PAT test.