vacuum forming/thermoforming elastic materials? I need to create few dozen opaque domes/hemispheres of various sizes from 80cm to 120cm.
The shape is pretty basic, example:
http://www.cmspinning.com/images/hemisphere_landing_large.jpg
The domes have to be foldable into smaller pieces for easy transportation and storage. Think heavy duty rubber gloves but just dome shape.

Would like to know if there are elastic sheet materials available to create these domes I could vacuum form like we can vacuum form rigid materials such as ABS plastic.

I understand there might be rubber domes available for sale so I wont waste time making my own but I'm going to make slight changes to the perfect dome shape so I need to make my own.

Possible candidates: TPE (thermoplastic elastomer), TPR (thermoplastic rubber), TPO (thermoplastic olefin), low density polypropylene, low density polyethylene, vinyl aka PVC, Polyurethane, EVA (Ethylene Vinyl Acetate). Some seller websites claim these can be thermoformed but there is next to none other source, video, etc. available online.
I'm not aware of any flexible rubbers which can be formed by vacuforming.  In my experience, when you start with a flat sheet of flexible rubber and press it against a mold, it pretty much returns to being a flat sheet of rubber when the pressure is released.

You can however cast flexible rubber (in liquid form) into a mold with your desired hollow hemisphere shape and then let it cure in the mold.  This will result in your hemisphere being the natural shape of the rubber to which it will return after each deformation.  

You will want to use a two part mold (one part to provide the outer shape of the bowl and the other to occupy the hollow interior while the foam is curing).  Two nesting bowls can be used together as the mold with the difference in the bowl sizes defining the wall thickness of your final rubber part.