Two little bottles with a brush in the cap start almost every seam-line argument on the bench: Tamiya Extra Thin Cement and Mr. Cement. Both are "capillary" glues — watery solvents that you flow into a join by touch rather than smear on like the thick tube glue of childhood — and both weld styrene into a seamless part. They run so close that the honest comparison is less about which bonds better and more about smell, dry speed, the brush in the cap, and what is on the shelf. Having catalogued the cements and seam tools builders actually reach for, here is how the two capillary standards differ.
The quick answer
Both weld plastic the same way and both do it well — you will not build a better model by choosing one over the other. Tamiya Extra Thin (the green cap) is the ubiquitous default: slightly milder, a lovely brush, and stocked everywhere. Mr. Cement flows a touch hotter and faster, and its Deluxe/quick versions add a finer brush for tight spots. Buy whichever your hobby shop stocks; if you are starting from zero, reach for Tamiya Extra Thin and never think about it again.
Head to head
| Tamiya Extra Thin | Mr. Cement | |
|---|---|---|
| Type | Capillary solvent cement | Capillary solvent cement |
| Application | Brush-in-cap, flows by capillary action | Brush-in-cap, flows by capillary action |
| Bond | Welds styrene, seamless | Welds styrene, seamless |
| Flow / bite | Watery, controlled | Slightly hotter, faster |
| Set to handle | A few minutes | Comparable, marginally quicker |
| Brush | Excellent | Good; Deluxe brush is finer |
| Smell | Solvent, moderate | Solvent, a bit stronger |
How capillary cement actually works
This is the technique that makes both bottles worth owning. Unlike a gap-filling tube glue, a capillary cement is mostly solvent — it does not stick parts together so much as melt the two mating surfaces so they fuse into one piece of plastic. You dry-fit the parts, hold or clamp them tight with the seam closed, then touch the loaded brush to the join line and let the thin fluid wick along the seam by capillary action. A tiny bead of melted plastic squeezes out of a good join; once cured you sand that flush and the seam vanishes. Flooding the surface or brushing it on before you close the parts is the classic beginner mistake — it melts detail and leaves a mess. Both cements reward the same restraint.
The Tamiya Extra Thin case
Tamiya Extra Thin is the one most benches default to, and for good reason. The fluid is watery and controlled, the brush in the cap is genuinely nice to work with, and it is stocked in practically every hobby shop and big online store, so you are never hunting for it. There is also a quick-setting (black-cap) variant that grabs faster for when you do not want to hold a part as long. It sets firm in a few minutes and cures fully over a day. If someone asks for one cement to buy first, this is the boringly correct answer.
The Mr. Cement case
Mr. Cement, from the Mr. Hobby family, is the close rival and some builders prefer it outright. The standard Mr. Cement S flows a little hotter and faster, which can mean a slightly quicker grab; the Mr. Cement Deluxe adds a finer metal-handled brush that gets into tight recesses more precisely than a standard nylon brush. Trade-offs are minor: a marginally stronger smell and, in some regions, slightly thinner shelf availability than the Tamiya. If your shop stocks it or you like the finer brush, it is every bit as capable a weld.
Technique beats brand
The uncomfortable truth is that your seams will look identical regardless of which bottle you pick, because the result is set by technique, not chemistry. Clamp or pinch the seam fully closed before you apply — a gap the cement cannot bridge stays a gap. Flow, do not flood. Let a bead of melted plastic form, then walk away and let it cure hard before you touch it; sanding a soft seam just reopens it. The parts these cements join come off the runner first, so a clean two-stage cut and a tidy nub set you up for a tight seam — the whole cutting workflow is in how to remove nub marks without stress whitening. To see the runner and gates these parts start on, spin the sprue tree on the bench.
After the glue: killing the seam
Welding the seam is only half the job — the cured bead has to be sanded flush and the faint seam line polished away. Foam sanding sticks stepping up through the grits erase the ridge and blend the join into the surrounding plastic without flat-spotting the part; a GodHand Kamiyasu sanding stick set is the bench standard for exactly this. Which grits to keep on the bench, and when to switch to a hard file, is covered in best sanding sticks and files for nubs. This step is why cement matters most on higher-grade multi-part kits — a Master Grade 1/100 kit has the split-half weapons and armor where a welded, sanded seam separates a clean build from a toy-looking one; a snap-fit High Grade may need almost none.
Ventilation note
Capillary cements are volatile solvents, not craft glue. They evaporate fast, and that vapor is what you smell — work in a ventilated space, keep the cap on between uses (the thin fluid also evaporates out of an open bottle), and do not huddle over an open bottle for an hour. This is milder than airbrushing lacquer, but "milder" is not "ignore it": a cracked window and some airflow are the baseline for any solvent cement.
The verdict
Tamiya Extra Thin and Mr. Cement are two excellent capillary cements that do the same job to the same standard, and no build has ever been ruined by picking the "wrong" one. Tamiya Extra Thin wins on availability and an easy-going brush, which makes it the right default and the one to buy first; Mr. Cement earns its fans with a slightly faster bite and, in the Deluxe, a finer brush for tight work. Own whichever your shop stocks, learn to clamp-flow-cure-sand, and your seams will disappear either way. See where kit-building tools rank on our best-of hub, and settle the grade question in RG vs MG Gunpla.
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Questions builders ask
Is Tamiya Extra Thin or Mr. Cement better?
They are effectively tied. Both are capillary solvent cements that weld styrene into a seamless part, and your finished seams will look the same with either. Tamiya Extra Thin wins on availability and has a lovely brush, making it the safe default; Mr. Cement flows a little hotter and faster, and its Deluxe version adds a finer brush for tight spots. Buy whichever your shop stocks and focus on technique instead.
What is capillary cement and how is it different from normal glue?
Capillary cement is a thin, watery solvent that you flow into a seam rather than smear on. Instead of gluing parts like a sticky adhesive, it melts the two mating plastic surfaces so they fuse into one piece. You hold the seam closed and touch the brush to the join, letting the fluid wick along by capillary action. Ordinary tube glue is thick and gap-filling but messier and weaker on a clean seam, which is why modelers prefer capillary cement for welding.
Do you sand after using plastic cement?
Yes, on any seam you want to disappear. A proper capillary weld squeezes out a small bead of melted plastic along the join; once it has cured hard, you sand that bead flush and polish out the faint seam line with progressively finer grits. Sanding too soon, while the plastic is still soft, just reopens the seam, so let it cure fully first. Foam sanding sticks are the usual tool.
Is plastic cement safe to use indoors?
It is fine indoors with basic ventilation, but treat it as a solvent, not a craft glue. The fast-evaporating fluid gives off vapor you should not breathe concentrated, so work near an open window or with some airflow, keep the cap on between applications, and avoid hunching over an open bottle for long stretches. It is much milder than airbrushing lacquer, yet it still deserves a ventilated bench.
