Thank you so much, that’s incredibly helpful! I might make my own case so i should be able to get around the size issue but you make a good point that there’s not much wriggle room if the harp’s already at 21cm! In case helpful to you, if you wanted to go beyond bubble wrap, i found this on how to layer up a bespoke foam casing which I think you could do without the additional lining and casing that this person also does: https://www.instructables.com/Make-a-Hybrid-Instrument-Case/?amp_page=true