The Best Airbrush Thinner and Additives
Water thins paint. It also strips out everything that made the paint work. That is the whole reason thinner exists.
The short answer
A dedicated airbrush thinner like Vallejo Airbrush Thinner is the right default: it dilutes hobby acrylics without diluting the binder, so paint still bonds and sprays without tip dry. Liquitex Flow Aid is the cheapest worthwhile addition if you only want one bottle of chemistry on the desk.
The quick version
| # | Product | Best for | Score | Price |
|---|---|---|---|---|
| 1 |  Vallejo Airbrush Thinner (71.261)A purpose-made thinner that holds flow and adhesion where water just dilutes the binder. The difference between tip-dry every pass and a clean session. | Thinning acrylics properly | 9.0 | Check price on Amazon |
| 2 | Liquitex Flow AidAn artist-grade flow improver that goes into distilled water, not straight into paint. A few dollars buys a lot of sessions. | The cheapest flow upgrade | 8.8 | Check price on Amazon |
Scores are our own editorial read against the criteria stated below — not a lab measurement and not a user rating. Tap a row for the full write-up.
Why water alone causes problems
Hobby acrylic is pigment suspended in an acrylic binder, plus additives that control how it flows and how fast it dries. The binder is what makes paint stick to the model.
When you add water, you dilute all of it — pigment, binder and flow agents together. Push that past roughly 25% and you get paint that looks right in the cup and behaves badly on the model: patchy coverage, a surface that rubs off under a fingernail, and pigment separating in the cup while you work.
A dedicated thinner replaces the water fraction with a carrier that keeps binder concentration and flow properties closer to where the manufacturer set them. That is the entire pitch, and it is why thinner is not a premium version of water.
How we picked
- Does it prevent tip dry? Paint drying on the needle tip mid-session is the most common airbrush annoyance and the clearest difference between water and a retarder-bearing thinner.
- Does adhesion survive? A thinner that lets you dilute heavily without the coat becoming fragile is doing its job.
- Compatibility across brands. Most hobby acrylics are water-based acrylics, so a good thinner should not be brand-locked.
- Cost per session. You use these in drops; a large bottle lasts months.
What each bottle actually does
Airbrush thinner. The general-purpose dilution medium. Usually water plus a flow improver and a mild retarder. Use this as your default.
Flow improver / flow aid. Reduces surface tension so paint levels out instead of beading. A few drops make thinned paint behave noticeably better — useful on the brush as well as through the airbrush.
Retarder. Slows drying. Fixes tip dry on hot days and keeps blends open longer. Overdo it and the coat stays tacky for an uncomfortably long time.
Airbrush cleaner. Not a thinner. It is formulated to dissolve dried acrylic and must never be used to dilute paint you are about to spray.
Isopropyl alcohol. A cleaning option, not a thinning one. It attacks the binder, which is exactly what you want for cleaning and exactly what you do not want in the cup.
Starting ratios
Consistency, not ratio, is the actual target — brands differ enormously in how thick they arrive. Use these as starting points and judge by how the paint runs off a stirrer:
- Basecoats: roughly 1 part thinner to 2 parts paint. Should run off a stirrer like skim milk.
- Glazes and gradients: 1:1 or thinner. Nearly transparent, built in passes.
- Acrylic primer: often nothing at all. Airbrush-ready primers are sold at spraying consistency; adding thinner is how you get a primer that does not grip.
- Washes through an airbrush: rarely a good idea, and never a substitute for brushing a wash into recesses.
The technique around all of this — testing on card, reading the spray pattern, fixing splatter — is in how to thin paint for an airbrush.
Three mistakes worth avoiding
Thinning primer. Airbrush-ready primers like Vallejo Surface Primer are already at spraying consistency. Diluting them produces a coat that paint lifts straight off.
Mixing cleaner into paint. Airbrush cleaner in the cup gives you a coat with no binder integrity. Cleaner is for cleaning.
Chasing a ratio instead of a consistency. A 1:1 mix of a thick paint and a 1:1 mix of an already-thin paint are two completely different liquids.
The picks in full
Vallejo Airbrush Thinner (71.261)
A purpose-made thinner that holds flow and adhesion where water just dilutes the binder. The difference between tip-dry every pass and a clean session.
What it gets right
- Keeps the binder working, so thinned paint still grips instead of pulling away
- Noticeably less tip-dry than water, which is the main thing that ruins a session
- The 500 ml bottle makes it cheap per use
Who it is wrong for
- Not a retarder — if your problem is paint drying in the nozzle, you also want flow improver
- Over-thin with it and you get the same transparency problem as with water
- Wrong product for lacquer or enamel paints; those need their own thinners
Scored against this page’s criteria
Specs from the manufacturer: Vallejo product page
We do not publish prices. Amazon shows the current one, which is the only one that is ever right. #ad · how this is funded
Liquitex Flow Aid
An artist-grade flow improver that goes into distilled water, not straight into paint. A few dollars buys a lot of sessions.
What it gets right
- Dramatically reduces tip-dry for a fraction of the cost of branded hobby additives
- An artist-shop staple, so it is easy to find and cheap in volume
- Works with any water-based acrylic, not just one brand's range
Who it is wrong for
- Must be diluted before use — neat Flow Aid in paint breaks the binder and the paint will not adhere
- Too much and paint beads and runs off the model
- Does not thin paint; it changes how paint behaves. You still need water or thinner
Scored against this page’s criteria
We do not publish prices. Amazon shows the current one, which is the only one that is ever right. #ad · how this is funded
FAQ
Questions people actually ask
Can I thin airbrush paint with water?
What is the difference between airbrush thinner and airbrush cleaner?
What ratio should I thin paint for an airbrush?
Do I need to thin airbrush primer?
What causes tip dry on an airbrush?
More in Airbrushing Miniatures and Models, or start from the beginning with what to buy first.
Sources
- Acrylicos Vallejo — airbrush thinner and Surface Primerchecked October 2026
- Anest Iwata-Medea — Eclipse and compressor specificationschecked October 2026