How about Wine Bottles, Instead of 2-Liter Pop Bottles.
You wouldn't have to worry about people stealing them for the return value.
You could still fill them with whatever you wanted - Hay, Dirt, Sand, Gravel, Cement or Water & still have the Load Bearing Factor & Thermal Abilities.
Let me change the subject at this point from Bottles.
An Idea I have been Interested in since I saw STAR TREK 5,
the one where they go back in time to get a whale & bring it back to the future.
Transparent Aluminum or Transparent Steel - Why Not?
I thought that it was a Brilliant Idea & with todays Technology I think it could be done - Why Not?
They have Memory Steel
now a days