Take a look at this video, and can you tell me what is the sheet he uses to make the plane?? foam (ie thermacol) or balsa wood??

Looks like laminated 10mm Biofoam / Depron.

I think it is 8-10mm foam board. The foam board is has two layers of paper on both sides with foam in the middle. This is more stiff than depron.
Cheers

Foam Board, known as Sunfoam/Sunboard in India, would be much heavier and wouldn't cut so easy with a modelling knife.

However, I could be wrong....................

VC bhaiya is right. I have this material, it is much heavier compared to depron and is also difficult to cut.

  Any replacement material for the same which will be lighter and easier to cut but at the same it stiff too..

i think its light weight rubber material which is used in making feather lite sandals

I think it is pink foam