TWSBI ECO Piston Filler Fountain Pen – Cosmo Blue Onyx

• Edition: Cosmo Blue Onyx — Premium Marbled Edition featuring swirls of nebula blue and green, ensuring no two pens are alike
• Nib: Black Onyx Steel — Precision Jowo stainless steel nib with a black finish to perfectly match the trim
• Filling Mechanism: Piston Filler — Internal piston draws ink directly into the barrel (approx. 1.76ml capacity)
• Ink Capacity: Massive — Holds nearly 4x more ink than a standard converter
• Body: Crystal Clear — Transparent barrel contrasts beautifully with the unique marbled cap and piston knob
• Maintenance: Fully Serviceable — Includes wrench and silicone grease for home disassembly
• Dimensions: 139 mm capped, 168 mm posted — Hexagonal cap prevents rolling and posts securely
• Origin: Made in Taiwan — Precision engineered for durability

About the TWSBI ECO Piston Filler Fountain Pen – Cosmo Blue Onyx

The TWSBI ECO Piston Filler Fountain Pen – Cosmo Blue Onyx is a stunning "Marbled Edition" inspired by the depths of interstellar space. Unlike standard solid colors, this model features a mesmerizing swirled resin on the cap and piston knob, blending deep Cosmic Blue with trails of Nebula Green.

Because of the unique injection molding process used for the marbled resin, no two pens are exactly alike—your pen will have its own distinct pattern. This cosmic aesthetic is grounded by the stealthy Onyx Black plated trim and a matching black nib, creating a striking contrast.

The ECO (short for "Economical") is famous for bringing high-end piston filling mechanisms to an accessible price point. The built-in piston allows you to fill the pen directly from a bottle, holding a massive 1.76ml of ink. The crystal-clear barrel allows you to monitor your ink level while showing off the unique colorway.

True to TWSBI’s philosophy of user empowerment, the pen arrives in a presentation box that includes a wrench and silicone grease, allowing you to fully disassemble and lubricate the mechanism yourself—ensuring your pen lasts a lifetime.