...you might just want to build your own superpressure balloon. NASA has been doing so for 10 years now and is able to lift an English ton of equipment 100,000 feet in the air and keep it there for over 3 months. Depending on the rate of lift and descent, I'd be fun to send a person up, never mind all the extra gamma-rays and extreme cold. (The extreme cold is nothing - we've got a polar air mass blowing into town this week.)
Unfortunately, the site is lacking in all those nagging details of construction. How are the various sections of film adhered together? How is the tendon attached? Since the ballon is going to get extremely cold, "Gorilla glue" just won't cut it. I'd guess a silicone. I'm also suprised that the helium doesn't diffuse out quicker, even knowing that diffusion coefficients are inversely related to temperature.