Uni-ball One P Refill Compatibility: The Best Gel Pen Setup with Signo

Do you have a pen you feel oddly attached to — the one you reach for whether you’re journaling, making lists, sketching, or traveling? For me, that used to be my Pentel EnerGel pen in 0.38mm. I relied on Pentel refills for almost three years because they were familiar and always worked well.

Then I started using the Uni-ball One P a few months ago and ended up carrying it everywhere. Naturally, I kept the Pentel refills inside it — until I recently found a refill that felt noticeably smoother and thinner the moment I tried it.

And the best part?
It fits the Uni-ball One P perfectly.

Today, I’m sharing that setup: the Signo UMR-82.

Why I Wanted a New Refill for My Uni-ball One P

In an earlier post, I talked about the Uni-ball One P and the alternative refills that could fit it. Since I write small and prefer thin, clean lines, the original Uni-ball refills were never quite the thickness I wanted. Thankfully, the Pentel refills I had been using for years fit the One P pretty well, so I didn’t feel the need to look for anything else at the time.

As my Pentel refills started running low, I knew I needed to buy new ones soon — and with the new planner season approaching, it felt like the right time to refresh my writing tools as well. Energel had been great for me and even helped me build a steady writing habit, but I sometimes wished the writing experience was just a little smoother. It wasn’t a big problem, but it was enough to make me curious about what else might be out there.

Of course, I wasn’t ready to give up the Uni-ball One P, so I went back to the compatibility chart and started looking for a new — and hopefully the best — gel pen setup that would work perfectly with it.

Uni-ball One P Refill Compatibility: What I Found

When I went back to the compatibility chart, I realized there were far more refill options for the Uni-ball One P than I expected. But not all of them fit what I was looking for. Some refills were known to write thicker based on reviews, some had feedback about feeling a bit scratchy, and others didn’t seem to sit as securely inside certain pen bodies. Since I write on narrow grids and prefer thin, controlled lines, those options didn’t feel right for me — at least on paper.

So I focused on refills that matched the qualities I prioritize: thin line width, smooth writing feel, a stable fit inside the One P, and reliable performance on Tomoe River paper.

That naturally narrowed the list down to just a few candidates. And among them, one stood out more than anything else — not just because it was compatible, but because the specifications matched exactly what I had been searching for.

My Pick: Signo UMR-82

Among all the compatible refills, the Signo UMR-82 (0.28mm) immediately caught my attention. I had never tried this specific refill before, but I’d always wanted to, and its reputation for a smooth writing experience — along with the specs that matched exactly what I look for in a thin gel refill — made it worth testing. So I ordered a single refill from JetPens just to try it out.

Signo UMR-82 Refill Review

First Impressions: Fit & Click

When the refill arrived, the first thing I checked was the fit inside the Uni-ball One P — and it was perfect. The UMR-82 sat securely in the pen body with no looseness or rattling, and the overall stability felt even better than the Pentel refills I had been using for years.

Another thing that surprised me was the click. Energel refills sometimes made a slightly stiff or squeaky sound when I clicked the pen, but the UMR-82 felt smoother and more solid inside the One P. It had that clean, satisfying click that makes a pen feel reliable the moment you pick it up.

Writing Experience: Thin, Smooth, and Shockingly Comfortable

What truly made me fall in love with this refill was how comfortable it felt during long writing sessions. When I write my journal, I can easily fill two or three pages. With the wrong pen, that leads to hand fatigue — something I experienced with Pentel refills a few times because of their slight friction.

With the UMR-82, the pressure needed to write is almost zero. The tip glides so naturally that I found myself writing more without realizing it. The lines remain clean and consistent, and the flow feels controlled but effortless. Even though it’s thinner than the pens I used before, it somehow feels smoother.

This was the biggest surprise of all: an ultra-thin 0.28mm refill that is actually comfortable for extended writing. I genuinely didn’t think that was possible until I tried the UMR-82.

How the UMR-82 Performs on Tomoe River & Midori Paper

This refill also passed two important tests: Tomoe River and Midori MD paper.

On Tomoe River, the ink didn’t smudge or feather. It created a crisp, clean line that looked sharp across the entire page.

On Midori MD, the smoothness of the UMR-82 becomes even more obvious. Midori MD has a slightly textured feel compared to Tomoe River, and many thin pens can feel scratchy on it. But the UMR-82 glided beautifully. This was the moment I realized how exceptional the combination of the One P body and the UMR-82 refill really is.

For planner users, especially those who write in Hobonichi, Midori, or Traveler’s Notebook inserts, this refill feels almost tailor-made. It provides precision without sacrificing comfort.

Signo Pens vs Other Thin Gel Pens (Why I Switched)

Over the years, I’ve tried many thin gel pens — mainly Pentel and Sarasa — and each had things I genuinely liked.

Pentel Energel was my longtime favorite because of its thin, consistent ink flow, and I relied on it for almost everything I wrote. But on Tomoe River paper, it sometimes smudged, so I avoided using it in planners like Hobonichi.

Sarasa, on the other hand, had decent ink performance but the pen body felt too thin for my hand, and I often felt discomfort during longer writing sessions. Even at the same tip size, Pentel still looked slightly thinner on paper, so I kept using it as my main setup.

But when I tried the Signo UMR-82, the difference was immediately noticeable. Among the three, Signo had the smoothest writing feel — thin and clean without scratchiness — and it dried the fastest on Tomoe River paper. It felt like the perfect balance between sharp lines and a soft, fluid glide.

The refill itself also goes into the Signo UT-1 pen body, which has a simple, clean black design. If you don’t want to use the Uni-ball One P, the UT-1 is a great alternative on its own.

It’s been almost two weeks of writing with the UMR-82 every day, and honestly, I don’t see myself going back to Pentel anytime soon.

Bonus: My New Coffee Color Uni-ball One P Body

Alongside my refill upgrade, I added a new Uni-ball One P body to my collection: Coffee. Paired with the Rose Gold I already owned, the two pens look adorable together. The warm tone of the Coffee version complements the thin, crisp lines of the UMR-82 perfectly.

It’s one of those setups that not only works well but also looks cute on a desk or planner spread.

Final Thoughts: The Best Refill Choice for the Uni-ball One P

After a couple weeks of testing, I can confidently say that the Signo UMR-82 is the best refill I’ve tried for the Uni-ball One P. It checks all the boxes: smoothness, thinness, comfort, and compatibility. It turned my writing routine into something I genuinely enjoy.

If you’re curious about Uni-ball One P refill compatibility, or if you want the best gel pen setup for planners, journals, or everyday writing, this combination is worth trying. I started out simply wanting a refill that felt better, but I ended up finding the setup that makes me look forward to writing every day!