"Guter Stoff" in German does not just mean a good (quality) fabric, it can also be used figuratively - either for something good to write about, or "Stoff" is also a slang word for drugs. Which means that guter Stoff is also a good drug.
If you know about these extra figurative meanings, it makes it sound much funnier when the Hansemuseum, in preparation for their next exhibition "Guter Stoff" is asking "Gebt uns euren Stoff" - give us your fabric. (Or share your drugs with us.) They are looking for items of clothing (or other fabric pieces) that have a history - or, to put it another way, that provide "guten Stoff" to write about. One piece will be chosen to be part of the exhibition itself, in the section about sustainability, and other items and their story will be shown on the website.
If you have an old item of clothing in your closets, and would like to participate, you can find the email to send your photo and story here on the museum website - the section is in German only, but sending your mail in English will be no problem for the team.