interfacing

I bought a purse pattern called the Paddington Satchel from Moonshine designs by Monica Poole (Australian) and it calls for a fusible interfacing called Volumenvlies. Anybody have any idea what weight that is? Because the pattern has a curvy front flap, I don't think it's as heavy as ultra-firm or peltex. I think what I have is either decor bond or craft bond. Suggestions would be greatly appreciated.