TWSBI Fountain Pen VAC Mini

The TWSBI VAC Mini is a pocket-sized fountain pen with vacuum filling – a mechanism that draws up to 2 ml of ink into the crystal-clear acrylic resin body with a single stroke. The lightly faceted, transparent barrel reveals the piston rod as it glides visibly through the shaft during filling. It features a stainless steel size-5 nib in extra-fine (EF) – precise enough for tight handwriting, micro-lettering and small-format notes where every line needs to be rendered cleanly.

Features

• Vacuum filling with shut-off valve: The piston works via negative pressure – nib in the bottle, press the piston, done. The integrated shut-off valve isolates the ink during transport and prevents pressure fluctuations that can cause leakage during flights or in warm bags.
• EF stainless steel nib (Size 5): Fine-engraved steel nib with narrow line width – ideal for small handwriting, narrow-lined notebooks and crosswords where wider nibs would feather. Gentle feedback on the paper surface with consistent ink flow.
• Ink capacity approx. 2 ml: Unusually generous for a pocket-sized pen – comparable compact fountain pens often use cartridges that hold barely 1 ml. The VAC Mini fills with a single hand movement and writes correspondingly longer.
• Transparent demonstrator barrel: The clear acrylic resin shaft makes the fill level readable at any time and shows the vacuum rod in all its mechanics. Lightly faceted profile that feels comfortable in the hand and is less sharp-edged than classic diamond cuts.
• Screw cap with posting threads: The cap screws firmly onto the rear end of the shaft with one-and-a-half turns – even with the valve open. Posted operation provides a balanced grip length equivalent to that of a full-size fountain pen.
• Maintenance-friendly design: The pen body can be completely disassembled. Replaceable nib unit (nib, feed, collar as one unit), replaceable O-rings, tool-assisted service. Spare parts are available separately.

Use & Tips

• Open valve before extended writing sessions: The shut-off valve seals the nib and feed. For more than a few lines at a time, loosen the cap at the rear slightly – otherwise the resulting vacuum will interrupt ink flow. Short notes work even with the valve closed.
• EF and paper: The EF nib shows its sharpest lines on smooth, calendered paper. On paper with good ink resistance and low absorbency, the line remains precise without fraying. On highly absorbent papers, the line may appear wider than expected.
• Ink choice for the EF nib: Well-flowing, water-based fountain pen inks work reliably. Very viscous or heavily pigmented inks (e.g. iron gall-based) should be tested for compatibility with acrylic resin and O-rings before use. Not document-proof – unsuitable for documents of permanent value.
• Cleaning: The vacuum system holds ink effectively back – which means rinsing requires a bit more effort than with cartridge-converter pens. Easiest method: fill and empty with clear water several times; for stubborn ink residue, disassemble the pen and clean individual parts separately.
• Travel and air travel: Close the valve completely and screw the cap on firmly – the VAC Mini is then well protected against pressure-related leaks. Recommendation: travel with the pen completely full (not half-full), as a full reservoir leaves less air space for expansion.
• Posting for small hands: Unposted, the VAC Mini offers a compact, sufficiently long grip section. Those who prefer more balance or have larger hands can screw the cap on the rear – this extends to standard length without becoming top-heavy.

For Fountain Pen Enthusiasts

The VAC Mini uses a vacuum filling principle: when the piston is pressed down, negative pressure is briefly created at the lower dead centre, which instantly sucks ink into the shaft – all in one stroke. This distinguishes the mechanism from the classic piston filler, where ink is slowly drawn in by twisting. The integrated O-ring valve at the piston end completely seals the feed and nib when the rear cap is closed. The VAC Mini's nib unit (nib, feed and collar) is identical to that of the TWSBI Classic and can be swapped as a complete unit by unscrewing the grip section – a nib change without special tools. The size-5 stainless steel nib is proportionally tuned for the body and does without the full mass of a size-6 nib found in larger TWSBI models.

Technical Specifications