ROCKLER SILICONE GLUE BRUSH

Finally, a glue brush that youll never have to throw away! This brush features silicone bristles that are easy to wash with water, and quickly shed dried glue for long-lasting service. Theyre also spaced to hold plenty of wet glue, meaning less time dipping and more time spreading. Use the narrow dimension for edges and the wide dimension for faces. The paddle end can be used like a pen for finer detail work such as moldings, and for spreading glue into grooves and mortises. Also available from Rockler, the 3-Piece Silicone Glue Application Kit.

Still not convinced this is the best glue brush you will ever own? Check out the full review by Popular Woodworking Magazine.
The brush is very versatile with the silicone bristles on one end and the paddle applicator on the other. Its easy to clean without chemical solvents even fully dried polyurethane glue cracks and peels right off the bristles and re-using the brush is also friendly to the environment.
When it s time for a glue-up, simply riffle the bristles as you would a deck of cards to peel any dried glue off and restore the brush to pristine condition. Unlike traditional brushes, this one wont shed bristles into your bead of glue. The brush is a generous 1" wide with 1/2" depth of bristles which are spaced to hold plenty of wet glue, meaning less time dipping and more time spreading. Since the brush is designed to last, it provides some additional features as well: The paddle end opposite the bristles can be used like a pen for finer detail work such as mortise and tenon, dovetail, and box joints, or like a spatula for spreading glue into grooves and mortises. The entire brush is waterproof, so rinsing thoroughly with warm water makes cleanup easy when glue is wet.
Technical Details:

Silicone Glue Brush measures 7 long.
The tapered brush tip measures 1 wide x 1/2 deep.
Completely waterproof - just soak it in water after your glue-up.