After a bit of googling, here is a likely looking cyclo-olefin with good transmission at UVC germicidal wavelengths (260nm):
And the graph above is for a 3mm thickness! How much thinner can we go I wonder for our balloon?
It's actually pretty hard to find out what weather balloons are actually made of. Anybody know? You just buy one - for $45! This is an amazing and fun hobby I think, as long as you are not near a major air traffic corridor.
I am aware I seem to becoming obsessed with UVC illuminated balloons. But maybe this is no bad thing! This is where the biology has led us. There is no point, IMHO, building a high altitude bioprospector unless you are stone cold certain it is itself sterile.
Come the new week I think I will ring Zeonex's European office and see how game they are!
Questions I will ask:
How much does this stuff cost?
What is the sheet size?
How does one stick it together? (A thermal crimp etc?)
Can they make the entire structure for us - at a cost?
If it is cheap to make then we can burst our balloon at altitude like most normal balloon flights. If it is expensive then we find some way of reusing the balloon, for instance by letting the helium out gradually through a valve. Presumably the valve would sit in an invagination in the cyclo-olefin to allow it to be UVC-illuminated.
Bed now I think! :-)