There are a number of materials without a perfect match in the existing database, especially recycled alternatives. Until the database is expanded to include more of these, the options are to:
Pick the closest match from the available emissions factors as a proxy.
Do your own research to see if there is a credible source that has calculated the emissions factor of a more similar material and reach out to Change Climate for review and approval to make a custom CO2 entry in your workbook.
Get independent support to conduct a life cycle assessment for your product or materials. Reach out to the Change Climate team to enable a Custom CO2 entry.