I use it for a Fernandes RB-80 bass guitar (copy of Rickenbacker 4001) and it fits really nice. The case is very light (3,8kg). Maybe it doesn't sound much lighter than a regular case of 5 kilos, but it makes a big difference. Perfect when commuting and on the Go.
The "foam" seems very sturdy, feels like styro. Regarding the materials, there's a caution tag on it (from California) saying the bag is made from harmful chemicals (not specified which chemical(s).. and I think I'll risk it!)
Only drawback I can think of is you can't carry it on your back, as there's only a shoulder-strap and the regular handles.