I posted this on another board for someone who had problems getting forearm growth...
Forearms can be a tricky area to develop...here is what I found that works for me...
Hammer Curls-either cross body or regular
Reverse BB Curls
Those 2 should work well for the brachioradialis\brachialis, pick one each session and go with it...also you can use the cables for either if you stagnate..sometimes I like to do 1 arm rope hammer curls
I have found that the extensors are often neglected, and many times this is why people have problems growing the flexors, because the body wants to prevent an imbalance...
The Reverse BB curls should hit them to some extent...but here is an exercise I will do every once in awhile..
Grab a fixed weight BB(easier to balance in the position it needs to be in)...start out pretty light on this...then do a front raise with it while standing, now holding that position do a reverse wrist curl motion
Actually I think forearm type curls are kind of overrated, for the flexors though I like BTB wrist curls and DB wrist curls when one is in a concentration curl position
Gripping strength can also translate to forearm size...work on these aspects of grip
-Pinching-plate pinches
-Crushing-COC grippers
-Holding-static holds with BB or DB, farmer's walk
I did some forearm exercises after my arm workout...here is what I did
Reverse BB curls
Plate pinches
Static Hold with Thick Bar
Farmer's walk with DB
BTB wrist curls
I stopped working mine directly except for a hammer curl\reverse curl type motion, I think they might have even grown a bit...so be careful not to overwork them...
This may look like a lot of work.but I don't goto complete failure on most of the exercises... I've found that it works for me...
My forearms are at 15" at 5' 8" 210-215lbs...would like to add 1\4"-1\2" in the next few months
Sorry for the long post!