We're not talking superfluidic Helium here... Glass or BPA should be fine... In that case the envelop is rigid and we might at well just suck out enough air to get buoyancy.
When I was reading about Sterling engines, people talked about H2 leaking straight through the steel walls of the container. I can't find a similar reference for helium, but it's conceivable, to a non-expert anyway. No superfluidity required.
Helium doesn't need to be superfluid to leak through a lot of materials. If you are designing a ultra high vacuum system you better make sure the type of glass you use doesn't leak He. Or if you get the chance to play with a mass spectrometer you can inhale helium and observe how it leaks through your chest.
