writes:The river products in the Battlefield in a Box range must be top-sellers, because it took me over a year on back-order to get these!
And as you can see, I still haven't been able to get the basic river set. But I have river bends, so I can make a very bendy river if I need to. 
When you open the thin cardboard box, you can pull out what looks like a stack of styrofoam sheets, taped together. Slice the tape and pull it loose, and the sheets turn out to be cocoons holding the river pieces.
So when you get everything unwrapped and discard the packing materials, you've got three river bend pieces and one ziploc bag of static grass (probably stuck to the bottom of one of the river pieces).
The river bends are made from the same stiff but flexible material that the manufacturer uses for its roads, fields, etc., and are painted back on the backside.
The pieces are roughly 12" tall and wide, with the river width being 2" to 2½" mostly, but over 3" on the widest part.
The river surface looks glossy in the pictures, but is matte to the touch. There is some dust and fiber that you may want to carefully wipe off.
It is up to the user whether or not to apply flock, and whether to use the bag provided or some other product that might best match your tabletop. They look rather barren as-is.
According to the box, the scale is "25-35mm scale." I'm showing a river bend piece here with 15mm Team Yankee models.
One box will make a bendy river three feet down your wargaming table. Intended to be mixed with the regular river pieces from Battlefield in a Box.