erik J posted a comment on my recent blog post about using trash bags instead of latex balloons:
From experience, the only problem is that they will leak more Helium, well at least comparing cheap plastic waste bags with the ~$20 balloons I bought. This is only a problem if you want to keep the camera up with the same balloon multiple times over several says. Would be nice to know more what you found, maybe you bags are better than mine, and I’m guessing you have free helium in that machine hall.
This might be useful information for some of you working with balloons. My response:
Actually I found that the party balloons I bought wouldn’t fly after staying inflated overnight. The other nice thing is that the balloons got stretched out and delicate after leaving them inflated, whereas I could just top off the trash bag a couple days later… it lost about 30-50% of its helium after 2 days.
Oddly, the party balloons didn’t seem to be smaller the next day, but they had less lift. I wonder if somehow they filled with air, or something. But maybe they were smaller and I just didn’t measure.
I wonder if actual weather balloons instead of party balloons are less porous.
I bought industrial trash bags, and they're pretty thick, like 2.7mil. You can buy 1.5 mil 98 gallon bags which would halve the weight, roughly, per volume, but they might be less durable, more porous.
Anyways I've put up some notes and links on this on the wiki: