Hello every one,
i have an idea,reinforcing thermocol  with 1-2mm  balsa wood strips on critical areas such as under the wings
as i don't have depron or any other foam used for this hobby
please suggest any other ideas,
and if having a supply of depron please comment

please read below thread it gives one an idea on how to build thermocol wing.

http://www.rcgroups.com/forums/showthread.php?t=306795

wing reinforcement and stuff depends on various things like wing loading, thermocol density, wing size etc. same goes for rest of the airframe parts  

I used a 1.5x6mm balsa spar in my 36" span 6mm depron wing of my Spitfire.
Was not enough to stop flexing.
Had to add 1/2" fibreglass to top and bottom.
Moral: Balsa spars not enough for foam wings!

I have used Balsa spars to support my foam wings for some time now.  In fact most of my wings are made out of commercially available thermocol and hence it requires good support.  Yes I do most aerobatics on these models and they do go through a tough time pulling at least 3-4 "G".
OK.. here is the method.  I generally use a 4 mm x 6 mm spar on top and bottom surfaces of the wing.  In the centre section I give a vertical member along the spars to the length required as per the wing to give the strength.  I did break a wing in the beginning but now I have no problems.  For my aerobatic model I use a vertically placed spar of 4 mm x 10 mm on top and bottom surfaces of the wing and then I give a centre hard wood or a 4 mm ply doubler for added strength. 
Yes all these spars are pasted by using normal Araldite as I do it in the night and the next day the joint is dry.
I also cover the centre portion of the wing is covered with a fibre glass cloth with epoxy (slow drying araldite).  This is to about 6-8 inches from the wing centre.
In the end I either cover the wing with paper pasted with diluted fevicol or normal tape and then covered with Vinyl or some good sheet.
As I make my own spars from Balsa sheets I have no problems in making any size I want.
Try it... its a good and effective way of doing it.

@shobhit17,
Sir, Dhajjiyan uda deen
I was only responding to the query about 1-2mm balsa spars, (presuming 36" foamies), not proper I-Beam spars with vertical grain shear webs! After all you and i have grown up with balsa D-tube wings where the thermocol itself is not required.

In retrospect, i find that my response was too simplistic, but perhaps ok for sub 36" foamies.

For larger models like yours, a link to one of your old posts about paper covered would have helped him.
Regards.

True... Balsa need to be thick enough to take the load of the wing forces.....