What type of wood and material should I use for a polyurethane mold?

I'm looking to make thin (about 1/4") pieces for a project that I am doing, and I was wondering what type of wood is good for making a mold. Also, what type of urethane should I look at for medium flexibility (can bend a bit to bend around a surface). Also, I am looking for a material that can attach well with 3m tape. Any recommendations for where to purchase the materials? Any mold making suggestions are appreciated!

The mold is for whats known as "eyelids" for vehicles. Basically they are 3m tape-on covers for lenses that can be painted to match the car to give show car's a more aggressive look. You can see an example here... http://tinyurl.com/22jobe

Here's what you do: Use a flat piece of pine or birch 3/4" to 1" thick. Draw out the shape of the curved face or streetside of piece. Then glue a big square chunk carvable styrofoam to the back of the wood. Use a coping saw and sandpaper to shape the styrofoam along the edge of wood. You can use the sandpaper to shape the curves that you like. When it's done, use casting tallow to coat and harden the mold surface. Now you can pour resin and lay fiberglass over it to make the actual finished piece.

I probably could answer that question if I knew what the purpose was. 1/4" polyurethane is readily available. And, why do you specify polyurethane rather that other types of poly?