I'm trying to work with a compressed Fuel file, without having to expand everything at the same time. It looks like not all streams are created equally. I seem to need a File instead of a FileReference: saveToFile |zipStream fileRef| fileRef := File named: (FileSystem disk workingDirectory / (self fileName, '.zip')) pathString. fileRef writeStreamDo: [ :s | zipStream := GZipWriteStream on: s. repository := nil. FLSerializer serialize: self on: zipStream. zipStream close]. And materializing doesn't like this stream from: aFileName |zipStream fileRef theNew| fileRef := File named: aFileName. fileRef readStreamDo: [ :s | zipStream := GZipReadStream on: s. theNew := (FLMaterializer new materializeFrom: zipStream) root. zipStream close]. ^theNew How am I supposed to work with compressed Fuel files? Stephan