what material is best to use for making patterns?

[GentlemanArcher]

Patterns for riders and for bow forms?

I'm guessing the backer board (I'm talking about the heavy cardboard stuff that tool peg boards are made of) won't last very long.  

Thin plywood?

I want to make up a new bow form and would like to use a pattern and my router to make sure its completely even.

Thanks
GA

[wood carver 2]

MDF (medium density fiberboard) is good for pattern making. You can find it at building supply stores and it comes in thicknesses from 1/4" to 1 1/4". It's fairly cheap and will come perfectly smooth with a router after being cut.
Use a dust mask. It's dirty stuff and not good for your health. I'm allergic to the glue in it.
Also, some people use corian. Durable and easy to work with.
Dave.

[7 Lakes]

I use .050 glass.  I put tape on the back to mark everything out.  No need for a router just cut it out with the band saw and put it against the belt with 220 grit paper.

[2treks]

plexi-glass
aluminum
baltic birch plywood.
Thats what I use for my big patterns
I also will use 050 glass for smaller pats