Used oat hulls to fill the LensSack Pro. Works great and is extremely light. If you wanted greater stability one could use rice, dried peas, beans, etc., but at twice the weight. Bag is extremely well made with heavy duty zippers. As a precaution I used adhesive valcro to close shut the zipper flap to stop any accidental opening of the bag which would spew oat hulls everywhere. Used it immediately out the car window with great results. Its amazing at how well the car works as a bird blind. Don't know if I will ever use my Wimberly head with the bag. Its so light with the oat hulls that it rests easily on the half rolled up window.