TBH I don’t know all the technical details other than they work and allow carriage of a lot more dry ice. This all shows how little attention I’ve given to DG training in the past but happily I’m doing my annual refresher this week so will try to get some answers on Thursday! I do know that they have a lower sublimation rate which is presumably a comment on the level of insulation. This lower sublimation rate allows the gas to dissipate safely. I think.