Or perhaps try the beige wall foam with the foil face at Home Depot.  Peel off the foil, cut out "layers", glue them together (with spray can foam - Great Stuff) in a stack and sculpt the rough shape to exactly what you want.  When it is sanded smooth, wrap it with Saran Wrap, spray it with Pam, lay up BID over the mold and (if you like) wrap it again with Saran Wrap.
EZ to sculpt, EZ to lay up, EZ to dig out form .... Jim S.

Russell Duffy wrote:

You might try using the liquid foam.  Its comes in any shape you want, sands very easily and doesn't make as much mess as the pink foam I used to use.

Cheers,
Dave Leonard Thanks Dave.  To make the radiator ducts, I was actually thinking of doing this.  I figure I can wrap the core in plastic, tape the mouth of a kitchen garbage bad around the inlet side of the core, open a hole in the bottom of the bag, then fill it with foam.  My thought is that this will leave me with a nice ball of foam to be shaped.  Can anyone think of a better approach? Thanks,Rusty (I sure won't use expanding foam from the spray cans again) 
 

--
Jim Sower
Crossville, TN; Chapter 5
Long-EZ N83RT, Velocity N4095T