TWSBI Eco Fountain Pen - Cosmos Blue with Onyx Trim and NibA more atmospheric blue demonstrator The TWSBI Eco Cosmos is a piston filling fountain pen with a deep blue finish and black trim. It keeps the standard Eco demonstrator structure, but the darker swirling blue gives it a more atmospheric look on the desk. Underneath, its still the same high capacity piston filler designed for daily writing. What sets it apart High capacity piston filling system, for long writing session Smooth, reliable steel nib,