Uni NanoDia Colour Leads vs Uni Hi-Uni Pencil Leads Review: The UK's Best Mechanical Pencil Refills for 2026

Mitsubishi Uni is Japan's most celebrated pencil brand, and their mechanical pencil leads represent the pinnacle of graphite and colour lead engineering. In this review, we compare two of their finest products: the Uni NanoDia Colour Mechanical Pencil Leads, a vibrant set of colour leads that bring creativity to mechanical pencil writing, and the Uni Hi-Uni Pencil Leads, the gold standard in graphite mechanical pencil refills. Both are available from TTPEN UK and both represent the very best that Japanese pencil engineering has to offer.

Uni NanoDia Colour Mechanical Pencil Leads — Bring Colour to Your Mechanical Pencil

The Uni NanoDia Color Mechanical Pencil Leads 0.5mm, 3 Pack is a product that opens up a world of creative possibilities for mechanical pencil users. At £12.00 for a 3-pack, it offers Uni's legendary NanoDia technology in a range of vibrant colours, allowing you to colour-code notes, create colourful diagrams, and add visual interest to your writing — all with the precision and convenience of a mechanical pencil.

The NanoDia Technology

NanoDia is Uni's proprietary lead formulation that incorporates nano-diamond particles into the lead composition. These microscopic diamond particles serve two purposes: they dramatically increase the strength of the lead, reducing breakage even in fine diameters, and they improve the smoothness of the writing experience by reducing friction between the lead and the paper.

The result is a colour lead that is significantly stronger and smoother than conventional colour leads. If you've ever experienced the frustration of colour leads breaking constantly — especially in fine 0.5mm diameters — the NanoDia technology is a revelation. The leads write smoothly, break rarely, and produce vibrant, consistent colour throughout their length.

Colour Range and Applications

The 3-pack format provides three complementary colours that work well together for colour-coded note-taking and organisation. The colours are vibrant and clearly distinguishable, making them ideal for highlighting different categories of information, marking important passages, or creating colour-coded diagrams and mind maps.

UK students have found the NanoDia colour leads particularly useful for revision — using different colours to categorise information makes it easier to recall during exams. Professionals use them for annotating documents, marking up plans, and creating colour-coded project notes. Artists use them for preliminary colour sketches and planning compositions.

Who Are the NanoDia Colour Leads For?

The NanoDia colour leads are for anyone who wants to add colour to their mechanical pencil writing without sacrificing the strength and precision that NanoDia technology provides. Students, professionals, and artists will all find them invaluable for organisation, annotation, and creative work.

Price: £12.00 (3-pack) — Buy Uni NanoDia Colour Leads at TTPEN UK

Uni Hi-Uni Pencil Leads — The World's Finest Graphite Mechanical Pencil Refill

The Uni Mitsubishi Pencil Hi-Uni Pencil Leads 0.3/0.5mm are the mechanical pencil equivalent of the legendary Hi-Uni wooden pencil — the finest graphite leads available for mechanical pencils, period. At £10.00, they represent exceptional value for a product that is widely regarded as the gold standard in mechanical pencil refills.

Hi-Uni Lead Technology

The Hi-Uni leads use the same high-uniformity graphite formulation as the celebrated Hi-Uni wooden pencils. This proprietary formulation ensures that every millimetre of the lead delivers the same hardness, darkness, and smoothness — a consistency that is simply not achievable with conventional lead formulations.

The leads are available in 0.3mm and 0.5mm diameters, covering the two most popular mechanical pencil sizes. The 0.3mm leads are ideal for ultra-fine technical drawing and detailed illustration; the 0.5mm is the most versatile all-purpose size, suitable for writing, sketching, and general use.

Writing and Drawing Performance

The Hi-Uni leads write with extraordinary smoothness. Even the harder grades glide across paper without the scratchy resistance that characterises inferior leads. The graphite is dark and consistent, producing a line that is easy to read and erases cleanly. For artists, the Hi-Uni leads are a revelation — the consistency of the graphite allows for precise tonal control that is impossible with lesser leads.

The leads are also notably strong for their diameter. The Hi-Uni formulation includes a polymer binder that reduces breakage, making them particularly reliable in the fine 0.3mm diameter where breakage is most common with conventional leads.

Who Are the Hi-Uni Leads For?

The Hi-Uni leads are for anyone who uses a mechanical pencil and wants the finest graphite available. Artists, architects, engineers, students, and everyday writers will all notice the difference that Hi-Uni quality makes. If you've been using generic leads and want to experience what premium graphite feels like, the Hi-Uni leads are the definitive upgrade.

Price: £10.00 — Buy Uni Hi-Uni Pencil Leads at TTPEN UK

Side-by-Side Comparison

Colour or Graphite — Which Uni Lead Is Right for You?

Both the NanoDia Colour Leads and Hi-Uni Graphite Leads represent the pinnacle of Japanese lead engineering, but they serve different purposes. If you want to add colour and visual organisation to your mechanical pencil writing, the NanoDia Colour Leads are the finest colour leads available — strong, smooth, and vibrant.

If you want the finest graphite writing experience available in a mechanical pencil, the Hi-Uni Leads are the definitive choice — their legendary consistency and smoothness make every other graphite lead feel inferior by comparison.

• Uni NanoDia Colour Mechanical Pencil Leads 0.5mm 3-Pack — £12.00
• Uni Hi-Uni Pencil Leads 0.3/0.5mm — £10.00

Both are available from TTPEN UK with fast UK delivery. Visit www.ttpen.co.uk to browse our full range of premium Japanese pencil leads and mechanical pencils.

Final Verdict

Uni's NanoDia Colour Leads and Hi-Uni Graphite Leads are two of the finest mechanical pencil refills available in the UK market. Both use proprietary Japanese technology to deliver performance that far exceeds conventional leads, and both earn our highest recommendation. Visit TTPEN UK today to upgrade your mechanical pencil experience.