Originally Posted by jyasaki
They'd leak down really quick. Helium is a smaller molecule, so things that are airtight are not necessarily helium tight. Which is why a latex balloon filled with helium doesn't last as long as one filled with air.
Surprising how small Helium molecules are,
in the early days of deep sea saturation diving some divers wrist watches had the glass face crack on return back to surface pressure ,
helium had penetrated through the watches waterproof seals over time due to living under pressure for weeks on end ,
on return to surface pressure helium would still be trapped inside the watch still at bottom pressure causing the glass to crack
small helium relief valves were brought out to combat the problem .