At Animecon in the Netherlands, I found this booth selling new thermoplastics that work quite like Worbla but not completely.
CastFixx, CastFlex and CastForm have a fabric structure that makes them more sturdy, so you do not need to use the sandwich technique for durable armor (saves you a lot of material!). Also, CastFlex has a soft fabric on the backside- no more armor chafing off your skin! And their foams are just as great!
I got my hands on a test-set and tried out priming it - I will also have to try gesso soon.
So, this is how the materials react towards wood glue and filler. There is a small strip of worbla attached to each since this is what I will use for decorations (like in pic2)
I painted them silver because this color shows off the structure best. With 4 layers of woodglue, you can erase said structure though.
Maybe my little experiment helps someone choose the right material!
The materials can be seen and purchased at Minque.nl