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Water thins acrylic paint but also breaks down its binder, which is why thinned-with-water acrylic goes chalky and loses adhesion. An acrylic flow improver medium solves the problem differently: it lowers surface tension so paint spreads and levels without diluting the binder. The confusion starts because two different product types share the shelf. True flow improvers are surfactant additives used in small amounts; flow or pouring mediums are binder-based liquids you can add generously. This guide covers both, with six products currently sold on Amazon.com, so you buy the right one for hard-edge painting, staining, airbrushing or pouring.
Quick answer: For traditional brush painting, staining and glazing, the Liquitex Flow Aid is the standard additive; dilute it with water per the label before mixing it into paint. For flat, hard-edge color with a slightly longer open time, the Winsor & Newton Professional Flow Improver is the pick. Airbrush and miniature painters should choose the Vallejo Airbrush Flow Improver, and if you actually want to pour, the Mont Marte Flow Medium or the bulk Nicpro Pouring Medium are the right category.
Our Top Picks at a Glance
- Liquitex Professional Flow Aid, 118 ml — Best overall flow improver additive
- Winsor & Newton Professional Flow Improver, 250 ml — Best for hard-edge and flat color
- Vallejo Airbrush Flow Improver, 200 ml — Best for airbrushing and miniatures
- Mont Marte Premium Acrylic Flow Medium, 250 ml — Best budget flow medium for fluid art
- Artecho Pouring Effects Medium, 236 ml — Best small pouring medium with gloss finish
- Nicpro Pouring Medium, 2040 ml with pump — Best bulk medium for classes and large pours
| Product | Best For | Key Spec | Key Strength | Price Tier |
|---|---|---|---|---|
| Liquitex Flow Aid | Staining, glazing, brushwork | 118 ml surfactant additive, binder-free | Reduces film tension; staining on raw canvas | $ |
| W&N Flow Improver | Hard-edge, flat color | 250 ml additive, slightly slows drying | No color shift with W&N Professional acrylic | $$ |
| Vallejo Airbrush Flow Improver | Airbrush, miniatures | 200 ml, 1-3 drops per 10 drops paint | Reduces tip dry and clogging | $ |
| Mont Marte Flow Medium | Fluid art, thinning | 250 ml binder-based medium | Increases translucency without dulling color | $ |
| Artecho Pouring Effects Medium | Small pours, glazes | 236 ml, gloss finish | Doubles as a glossy top coat | $ |
| Nicpro Pouring Medium | Bulk pouring, classrooms | 2040 ml with pump | Huge volume, dries clear and crack-free per listing | $$ |
How We Chose
We did not mix or paint with these mediums for this comparison. Selections are based on the Amazon listing details and specifications checked in October 2026, on the well-established chemistry of acrylic additives versus binder mediums, on how each product’s format and volume suits its stated use, and on how widely each is reviewed by Amazon buyers.
- Product type: surfactant additive (use sparingly, dilute first) or binder-based flow medium (add freely).
- Stated use: brushwork, hard-edge, staining, airbrush or pouring.
- Effect on color and finish: whether the listing describes color shift, translucency or gloss.
- Volume and dispensing: small bottles for additives; large pump bottles for pouring.
- Safety labeling: ASTM D-4236 or non-toxic statements where present.
Best Acrylic Flow Improver Medium Options Reviewed
1. Liquitex Professional Effects Medium, Flow Aid 118 ml — Best for staining, glazing and brushwork
Liquitex Flow Aid is the reference product in this category. The listing describes it as a binder-free aqueous solution with surfactants, used with any acrylic medium or color when you want increased flow and absorption and decreased film tension and friction. Liquitex singles out staining effects on raw canvas as a strength.
Because it contains no binder, Flow Aid is an additive, not a medium you pour in freely. The label gives a dilution ratio with water; follow it, then use the diluted solution in place of plain water when thinning paint. Overuse can weaken the paint film, so measure rather than guess.
Best suited for: painters who glaze, stain raw canvas, paint watercolor-style washes with acrylic, or want brushstrokes to level on smooth panels.
Key features:
- 118 ml (4 oz) bottle
- Binder-free surfactant solution
- Reduces surface tension and friction
- Compatible with any acrylic color or medium
- Listed for staining on raw canvas
Pros:
- Industry-standard additive from a major brand
- A little goes a long way once diluted
- Works with watercolor as well as acrylic per the listing
Cons and limitations:
- Must be diluted; using it neat can compromise adhesion
- Small bottle
- Not a pouring medium
Buying consideration: Mix a batch of diluted Flow Aid in a labeled jar and use it as your “water” for the session; it keeps ratios consistent.
2. Winsor & Newton Professional Acrylic Flow Improver, 250 ml — Best for hard-edge and flat color
Winsor & Newton’s Flow Improver is aimed at painters who need flat, even areas of color. The listing says it increases flow without changing color strength, is effective for hard-edge techniques, maintains color stability and slightly slows drying. Used with Winsor & Newton Professional Acrylic it is described as giving no color shift from wet to dry.
The 250 ml bottle is more than double the Liquitex size, which matters if you paint large flat passages regularly. Like Flow Aid, it is an additive and the label specifies dilution with water before use.
Best suited for: geometric abstraction, sign painters, muralists and anyone frustrated by streaky flat fills.
Key features:
- 250 ml (8.4 oz) bottle
- Increases flow without reducing color strength
- Slightly slows drying for smoother leveling
- Suited to hard-edge techniques
- No wet-to-dry shift with W&N Professional acrylic
Pros:
- Larger volume than Liquitex
- Longer open time helps leveling
- From an established fine-art brand
Cons and limitations:
- Still an additive that must be diluted
- Not designed for pouring
Buying consideration: If your main problem is brush marks in flat shapes, this is the better choice of the two professional additives.
3. Vallejo Airbrush Flow Improver, 200 ml — Best for airbrushing and miniatures
Airbrushes clog when acrylic dries at the needle tip, and that is the problem Vallejo’s Flow Improver targets. The listing recommends 1 to 2, up to 3, drops per 10 drops of paint in the cup, and says it improves fluidity, delays drying, reduces tip dry and prevents nozzle clogging for a more uniform finish.
It is marketed to miniature, wargaming and scale-model painters, but the same benefit applies to fine artists who airbrush backgrounds or gradients. The 200 ml bottle is recycled r-PET plastic.
Best suited for: airbrush users, miniature painters and model builders who thin acrylic for spraying.
Key features:
- 200 ml (6.76 oz) r-PET bottle
- Dose: 1-3 drops per 10 drops of paint
- Delays drying and reduces tip dry
- Helps prevent nozzle clogging
- Transparent, matte listing finish
Pros:
- Clear dosing guidance on the listing
- Purpose-built for airbrush problems
- Large bottle relative to use rate
Cons and limitations:
- Not intended for brush painting on canvas
- Should be combined with a thinner, not used alone, for most airbrush mixes
Buying consideration: Use alongside an airbrush thinner; flow improver controls drying and tension, not viscosity.
4. Mont Marte Premium Acrylic Flow Medium, 250 ml — Best for budget fluid art and thinning
Here the category changes. Mont Marte’s Flow Medium is a binder-based medium, described in the listing as a pouring medium for thinning acrylic paints and mediums or diluting binders. It increases translucency without affecting color intensity, enhances flow and is described as great for fluid art.
Because it carries binder, you can add it generously without the adhesion risk of water or overused surfactant. For a beginner who wants to try pouring or make glazes from tube paint, it is an inexpensive 250 ml entry point.
Best suited for: beginners thinning tube acrylics for pours or glazes who want one bottle that does both.
Key features:
- 250 ml (8.45 oz) bottle
- Binder-based flow and pouring medium
- Increases translucency, keeps color intensity
- Gloss finish
- Non-toxic per the listing
Pros:
- Lowest price tier for a true medium
- Safe to use in larger proportions than an additive
- Versatile between glazing and pouring
Cons and limitations:
- Not a surfactant, so it will not reduce surface tension the way Flow Aid does
- Smaller volume than dedicated pouring jugs
Buying consideration: For pouring on more than a couple of canvases, step up to the Nicpro jug; for glazes and occasional pours, this bottle is enough.
5. Artecho Pouring Effects Medium, 236 ml — Best for small pours with a gloss finish
Artecho’s medium is another binder-based option in a translucent 8 oz bottle so you can see how much is left. The listing says it reduces viscosity and brush strokes, creates glazes, increases flow, smoothness, transparency and brightness, and can be applied over a dried painting as a protective glossy finish.
It conforms to ASTM D-4236 and EN 71-3 and is marked not suitable for children under three. For small pours on stones, boards and canvases, or as a glaze medium, it fills the same role as Mont Marte with the added top-coat use.
Best suited for: crafters pouring small pieces and painters who want a glaze medium that doubles as a gloss coat.
Key features:
- 236 ml (8 oz) translucent bottle
- Reduces viscosity, increases flow and transparency
- Usable as a glossy protective finish when dry
- ASTM D-4236 and EN 71-3
- Non-toxic per the listing
Pros:
- Dual use as medium and top coat
- Visible fill level
- Safety certifications stated
Cons and limitations:
- Small volume for pouring
- Not an airbrush or hard-edge additive
Buying consideration: A gloss top coat from pouring medium is not a varnish; use a proper varnish for UV protection on finished work.
6. Nicpro Pouring Medium for Acrylic Paint, 69 oz with Pump — Best for bulk pouring and classrooms
If you pour often, buying medium by the cup is expensive. Nicpro’s 2040 ml (69 oz) jug has a built-in pump for spill-free dispensing and is pitched at classrooms, workshops and artists who pour regularly. The listing describes it as reducing viscosity, increasing flow, transparency and smoothness, preventing colors from blending together, drying transparent and preventing cracks.
It is non-toxic, conforming to ASTM D4236 and EN71 per the listing, and the translucent jug shows remaining volume. Surface recommendations include canvas, stone, rock, wood, leather and metal.
Best suited for: teachers, paint-party hosts and dedicated pourers who mix medium by the cup rather than the teaspoon.
Key features:
- 2040 ml (69 oz) jug with pump
- Reduces viscosity, dries clear, crack-resistant per the listing
- Keeps colors from muddying
- ASTM D4236 and EN71
- Multi-surface
Pros:
- Best volume for the money in this comparison
- Pump makes consistent measuring easy
- Safety certifications stated
Cons and limitations:
- Heavy and bulky to store
- Overkill for glazing or occasional pours
- Not a surfactant additive
Buying consideration: Buy this only if you pour regularly. Opened medium keeps well, but a jug this size should be used within a reasonable time.
Buying Guide: How to Choose an Acrylic Flow Improver Medium
Flow improver additive vs. flow medium
A flow improver or flow aid (Liquitex, Winsor & Newton, Vallejo) is a surfactant with no binder. It is diluted with water and used in small quantities to lower surface tension. A flow or pouring medium (Mont Marte, Artecho, Nicpro) contains acrylic binder and can be added in large proportions to make paint fluid and translucent while preserving adhesion. Know which one your technique needs before you buy.
Dilution and dosage
Additives are concentrated. Liquitex and Winsor & Newton specify dilution with water on the label; Vallejo specifies drops per drops of paint for airbrushing. Too much surfactant produces a weak, sometimes tacky paint film. Mediums have no such ceiling, though very high ratios reduce color saturation.
Technique: brushwork, hard edge, staining, airbrush or pour
Brushwork and glazing favor Flow Aid. Flat hard-edge shapes favor the Winsor & Newton product for its slight drying delay. Staining raw canvas is a listed use for Liquitex. Airbrushing calls for Vallejo. Pouring calls for a binder medium, in a volume that matches how often you pour.
Color shift and finish
Additives are clear and should not change color; Winsor & Newton specifically claims no wet-to-dry shift with its own professional acrylics. Mediums increase translucency and most dry gloss, which can alter how colors read next to matte passages. Varnish evens that out.
Volume and dispensing
Because additives are diluted, 118 ml lasts a long time. Mediums are consumed by the cup, so 250 ml suits glazing and small pours while a 2 liter pump jug suits regular pouring and teaching.
Compatibility and safety
All six products are listed for acrylic paint; Liquitex also lists watercolor. Several carry ASTM D-4236 or EN71 conformance. Ventilate when airbrushing regardless of the additive.
Related Reading on Acrylic Mediums
Flow improvers are one of many additives. Our overview of what medium to use with acrylic paint explains gels, gloss and matte mediums, retarders and texture pastes so you can see where flow products fit. When a fluid painting is finished and fully cured, follow our guide to varnishing an acrylic painting to protect the surface.
Common Mistakes to Avoid
- Adding Flow Aid or Flow Improver straight from the bottle instead of diluting with water first.
- Using a surfactant additive as a pouring medium and ending up with a weak, cracking film.
- Thinning acrylic with large amounts of plain water, which breaks the binder; use a medium for heavy thinning.
- Expecting a flow medium to stop airbrush tip dry; that is the job of a dedicated airbrush flow improver.
- Treating a gloss pouring medium top coat as a varnish with UV protection.
- Buying a 2 liter jug for occasional glazing when a small bottle would be used up before it degrades.
FAQs
What does acrylic flow improver actually do?
It lowers the surface tension of acrylic paint so it spreads, levels and absorbs more evenly. Additives like Liquitex Flow Aid do this without adding binder, so they are used in small, diluted amounts.
Is flow improver the same as pouring medium?
No. Flow improver is a surfactant additive with no binder. Pouring medium contains acrylic binder and is added in larger amounts to make paint fluid for pours. Mont Marte, Artecho and Nicpro sell mediums; Liquitex, Winsor & Newton and Vallejo sell additives.
How much flow improver should I add to acrylic paint?
Follow the label. Liquitex and Winsor & Newton specify a dilution with water before use; Vallejo recommends 1 to 3 drops per 10 drops of paint for airbrushing. Overuse weakens the paint film.
Can I use water instead of a flow improver?
A little water is fine, but large amounts dilute the binder and can cause poor adhesion and a chalky finish. Flow improver thins and levels without that problem; a flow medium thins while adding binder.
Which flow improver is best for airbrushing?
The Vallejo Airbrush Flow Improver is formulated for airbrushes, reducing tip dry and clogging. Use it with an airbrush thinner to control viscosity.
Does flow improver change the color or finish of acrylic paint?
Additives are clear and should not shift color; Winsor & Newton claims no wet-to-dry shift with its professional line. Binder mediums increase translucency and usually dry gloss.
Final Recommendation
If you paint with brushes and want smoother flow, better staining and cleaner glazes, buy Liquitex Flow Aid and dilute it as directed. For flat, hard-edged color, the Winsor & Newton Flow Improver is the better fit thanks to its slight drying delay. Airbrush users should choose Vallejo Airbrush Flow Improver. If your real goal is pouring, skip the additives: Mont Marte Flow Medium or Artecho Pouring Effects Medium for occasional small work, and the Nicpro 69 oz jug if you pour every week.
