How to Choose the Right PU Pigment for Shoe Soles

A good PU pigment gives you the same sole colour on the hundredth batch as on the first. A poor one shows up as streaks, shade drift and rejected pairs.

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Colour is one of the first things a buyer judges on a shoe, and for a PU sole it starts with the pigment. This guide covers what to look for, how to match the pigment to your sole type, and where manufacturers usually go wrong. In short, the right pigment disperses fully, holds its shade under heat and light, stays consistent between batches and suits your sole density.

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What Is a PU Pigment, and How Is It Different from Dye or Masterbatch?

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A PU pigment is a finely ground colour particle mixed into a polyurethane system to colour the finished part. In footwear it usually comes as a paste, with the pigment already ground into a liquid carrier. You add it to the polyol side before it meets the isocyanate.

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Three terms often get mixed up:

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• Pigment: Solid particles that stay suspended in the material. They give good opacity and hold colour well under light and heat.
• Dye: Dissolves into the material. It can look bright at first, but it tends to migrate and fade faster.
• Masterbatch: Pigment pre-mixed into solid polymer pellets. It suits thermoplastics such as PVC or TPR. It does not suit PU, which is a liquid system that reacts as it cures.

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A PU sole pigment is used in direct-injection soles, unit soles and PU foam.

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Mixing PU Pigment vs Dosing PU Pigment: What's the Difference?

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Dosing and mixing are two different steps, and mixing up the terms causes real problems on the floor.

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Dosing is how much pigment paste goes into a batch of polyol. It is a measured quantity, set to reach a target shade. A dosing error, even a small one, shifts the shade from batch to batch. If you meter by weight or through a dosing pump, a small drift in that reading shows up as a visible shade change pair to pair.

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Mixing is what happens after dosing. It is how evenly the pigment paste spreads through the polyol before it reacts with the isocyanate. Get the dose exactly right and skip proper mixing, and you still get streaks, a mottled surface or one side of a sole darker than the other. Mixer type, mixing speed and mixing time all affect this step.

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So dosing sets the target shade, and mixing decides whether that shade shows up evenly across the sole. A batch can fail on either one, and the fix for each is different.

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For most sole makers running pigment paste for PU, check both steps separately. Weigh or meter every dose, and hold mixing time fixed for every pour rather than leaving it to an operator's judgment.

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What Makes a Good PU Sole Pigment? Key Quality Factors

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Check these points before you approve anything:

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• Colour strength. A strong pigment reaches the shade with less paste.
• Dispersion. Cast a thin sample and look for specks or streaks.
• Heat and UV stability. Soles face mould temperature first, then sunlight and washing. White, beige and pastel shades show yellowing and fading first.
• Migration resistance. The colour should not bleed into uppers, adhesives or neighbouring parts.
• Low moisture. Water reacts with isocyanate and forms bubbles in the sole.
• Batch-to-batch consistency. This matters most once you are in production. Shade differences between deliveries are a common reason soles get rejected, which we explain in why colour batches don't match.
• Compliance. Ask for documents showing the product is phthalate-free and ready for REACH, the European Union's chemical safety regulation. Export buyers often ask for this.

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How Do You Match a PU Pigment to Your Sole Type?

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Sole type changes how the same paste looks. Foam contains tiny air cells that scatter light, so a low-density sole looks paler than a dense one made with the same dose. A shade approved on a solid sample can look washed out on a foam sole.

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The base system matters too. Every PU system has its own natural tone, and that tone shifts the final colour. Dual-density soles need separate trials for the outsole and the midsole, since each has its own density and thickness.

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Always trial on your own system, at your own density, in your own mould. Our guide to colour matching for unit soles goes deeper on this.

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How Much PU Pigment Should You Use?

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Most pastes for PU are dosed in the low single digits as a percentage of the polyol by weight. The supplier's datasheet gives a starting range for each shade. Your trial sets the final figure.

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Over-pigmenting wastes paste and can affect how the sole cures or feels on the surface. In some cases the colour can rub off. Under-pigmenting leaves a thin, uneven colour that changes with sole thickness, and small weighing errors turn into visible shade shifts.

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Weigh every batch. Do not dose by eye or by scoop. Keep a record of the dose for each approved shade, and adjust in small steps when you tune a colour. A big jump overshoots the shade and wastes a pour.

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Common Mistakes When Choosing PU Footwear Pigment

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• Buying on price alone. A cheaper paste with low colour strength needs a higher dose, so the cost per pair may not fall. Weak consistency then adds rejects on top.
• Ignoring batch consistency. Some suppliers send a great first lot and a drifting third one. Ask how they check each lot against a retained standard.
• Skipping sample testing. A shade card is a starting point, not an approval. A tan that looks right in the lab can turn slightly pink on the line if the polyol batch or mould temperature changes. Only a trial on your own setup shows this.
• Judging colour under factory lighting. Tube lights hide differences. Check shades in daylight or a light booth.

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Why Manufacturers Choose Mittal Chemplast for PU Colourants

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Mittal Chemplast has worked on footwear colour since 1982. The Ansh range of PU colourants is built for footwear components, including soles.

Three things set the range apart:

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• In-house colour matching. In-house formulation experts match shades to your sample and develop new formulas when the shade card falls short.
• Consistent quality. Steady shades from lot to lot mean fewer rejections on your line.
• Dependable supply. You get the quantity you ordered, when you expect it, so production does not stall.

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Picking a PU pigment is easier when you can see it on your own sole. You can request a shade card or a free pigment sample from Mittal Chemplast and test it on your line.

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FAQs

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How do you match a PU pigment to different sole types?

Trial the pigment on your own system and density, since foam and solid soles show colour differently.

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Are PU pigments phthalate-free and REACH compliant?

Many PU pigments are made to be phthalate-free and REACH-ready, but you should always ask your supplier for documentation covering the exact product you plan to use.

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Can I get a custom shade matched to my sample?

Yes, Mittal Chemplast's colour team can match a shade to your sample and develop custom colours when the standard shade card does not have what you need.

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What causes colour variation in PU soles?

Colour variation usually comes from inconsistent pigment batches, weighing errors, changes in polyol or mould temperature, and differences in sole density or thickness.

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How much pigment paste do I need per batch?

Most pigment pastes for PU are dosed in the low single digits as a percentage of the polyol by weight, so use the supplier's datasheet as a starting range and confirm the final dose with a trial.

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