The TWSBI ECO fountain pen in Transparent Blue features a clear acrylic body and transparent blue cap and turning knob, silver trim, a piston ink-filling system, smooth-writing steel nib and a screw-on cap. The TWSBI ECO piston ink-filling system uses only bottled ink and the clear body allows the user to view the level of ink remaining in the pen at all times. The pen cap has an inner cap liner that maintains a thorough seal when the pen is not in use.

The traditional mechanism of the fountain pen, combined with a modern industrial design, embodies both the past and the present. This pen runs about the same in length as the Diamond 580 and is just a tiny bit thinner. One difference between the ECO fountain pen and the other TWSBI pens is that the ECO does not have a removable nib unit, and the barrel and nib unit are all one piece. There will not be separate nib units for this pen.