Matsui Under Base Blocker 301 Gray — The Invisible Shield Between the Garment and Your Ink

You printed a beautiful white on a red polyester polo. It looked perfect coming off the press. Twenty-four hours later, the white has turned pink. The red dye from the polyester fabric migrated through your ink and discolored it.

That is dye sublimation migration — and it is the #1 enemy of printing on polyester and synthetic garments.

Matsui Under Base Blocker 301 Gray exists to prevent it.

It is a carbon-based dye barrier printed as the first layer — before your whites, before your colors, before anything else touches the garment. Blocker Gray creates a physical and chemical barrier between the polyester fabric and your ink layers. Dyes from the garment cannot pass through the blocker. Your colors stay true. Your whites stay white. Your reds stay red instead of turning into a mystery color contaminated by the garment dye underneath.

The gray color is deliberate. A pure black blocker like Blocker Black LG creates maximum dye-blocking density but can darken the appearance of lighter top colors. Blocker Gray provides excellent dye migration control with a neutral gray tone that enhances top-color vibrancy on dark garments without the heavy visual influence of a pure black underbase. For most polyester jobs — especially those with lighter or medium-tone top colors — Gray is the preferred choice.

Works Under Plastisol Inks Too

This is the detail that changes the game for plastisol-focused shops.

Traditional plastisol dye blockers are thick, stiff, and heavy. They create a plasticky barrier layer that adds significant weight and stiffness to the print. The garment loses its soft hand feel. The print area feels like a rigid patch bonded to the fabric.

Matsui Under Base Blocker 301 Gray is water-based — and it works as an underbase under plastisol inks. Print the Matsui Blocker Gray first, flash it, then print your plastisol colors on top. The water-based blocker cures to a thinner, softer, more flexible barrier than traditional plastisol blockers — which means the entire print stack is noticeably softer and more flexible than a plastisol-only blocker plus plastisol color stack.

Why this matters: the blocker layer is always the heaviest, thickest layer in the print stack because it needs enough density to stop dye migration. With a traditional plastisol blocker, that heavy layer is stiff PVC. With Matsui Blocker Gray, that heavy layer is soft, flexible, water-based acrylic. The plastisol color layers on top are the same — but the foundation underneath is dramatically softer. The cumulative hand feel improvement is noticeable the moment you touch the garment.

For plastisol shops that print on polyester regularly — team jerseys, athletic wear, performance polos, and corporate apparel on poly blends — switching just the blocker layer from plastisol to Matsui Blocker Gray is the easiest, lowest-risk upgrade to softer prints. You do not need to change your entire ink system. You do not need to learn water-based color mixing. You change one layer — the blocker — and every polyester print in your shop gets softer.

The workflow for plastisol shops: Print Matsui Under Base Blocker 301 Gray → flash at 320°F → print your plastisol colors on top as normal.

When You Need a Blocker — The Complete Guide to Dye Migration

What is dye sublimation migration?

Polyester and many synthetic fabrics are dyed using sublimation dyes — dyes that bond to the fabric by converting from a solid to a gas under heat. This is how the color gets into the polyester fibers. The problem is that this process reverses when you apply heat during screen printing. When your dryer or flash unit heats the garment to cure your ink, the sublimation dyes in the polyester re-gasify and migrate upward through your ink layer and discolor your print. Red garments turn white ink pink. Blue garments turn white ink purple. Black garments turn white ink gray-green. The garment dye contaminates your ink from underneath.

This can happen immediately on press or over the 24–72 hours after printing, as residual heat energy in the garment continues driving dye migration. A print that looks perfect on the press can show dye bleed the next morning.

Which garments always need a blocker?

• 100% polyester — especially dark and bright colors
• Polyester blends with 50% or more polyester content
• Performance fabrics and Dri-Fit garments
• Sublimated garments such as all-over-print jerseys and polos
• Camo patterns on polyester

Which garments may need a blocker?

• 50/50 cotton/poly blends — always test first
• Dark tri-blends — test first
• Recycled polyester — test first

Which garments typically do not need a blocker?

• 100% cotton
• 100% cotton ring-spun and combed cotton
• Low-poly blends under 25% polyester, though dark colors should still be tested

The golden rule: if you are unsure, test. Print a small test sample, cure it, and check it 48 hours later. Dye migration can take up to 72 hours to fully show up.

Under Base Blocker 301 Gray vs. Under Base Blocker 301-LG Black

Both Matsui blockers stop dye migration. The difference is color, density, and how they affect your top colors.

The bottom line: Blocker Gray is the everyday workhorse — it handles the vast majority of polyester jobs with a neutral gray underbase that does not darken your top colors. Blocker Black LG is the heavy-duty option for the most aggressive dye migration situations. Most shops stock Blocker Gray for daily use and Blocker Black LG for problem garments. You can also mix your own Gray: 90% Blocker Black LG + 10% Matsui Stretch White.

Note: The 350 Series polyurethane system uses its own blocker — Under Base Blocker 350. The 301 Gray and 301-LG Black blockers are for the acrylic system and for plastisol compatibility.

The Blocker Print Sequence

For water-based top colors

• Print Under Base Blocker 301 Gray → flash at 320°F (160°C)
• Print Matsui white such as 301W-B, Stretch White, or EasyPrint White → flash
• Print Matsui color layers using bases plus Neo Pigments
• Cure at 320°F (160°C)

For plastisol top colors

• Print Under Base Blocker 301 Gray → flash at 320°F (160°C)
• Print plastisol white → flash
• Print plastisol color layers on top
• Cure at your standard plastisol cure temperature

The blocker layer replaces whatever blocker you were using before. The rest of your process stays exactly the same.

Additive Compatibility

For the color layers printed on top of the blocker, use the full Matsui additive lineup as normal — including Quick Additive in your base and pigment mixes. Browse the complete Matsui additive collection here.

Why Screen Printers Choose Under Base Blocker 301 Gray

I print on polyester jerseys and performance wear — my whites keep turning pink and purple.

This is dye sublimation migration, and it is the core problem Blocker Gray solves. Print Blocker Gray first, flash, then print your whites and colors on top. The blocker creates a barrier that stops garment dyes from contaminating your ink. Whites stay white. Colors stay true.

I use plastisol inks and want softer prints on my polyester jobs.

Switch just the blocker layer from plastisol to Matsui Blocker Gray. Print the water-based Blocker Gray first, flash, then print your plastisol colors on top as normal. The water-based blocker cures softer and more flexible than a plastisol blocker, so the entire print feels noticeably softer.

My prints look clean off the press but show dye bleed the next morning.

This is delayed dye migration. Blocker Gray stops this by creating a barrier that prevents garment dyes from moving into your print, whether the bleed happens immediately or over the following days. Always test 48 hours out to confirm complete blocking.

I print on sublimated garments and the sublimation dyes contaminate my screen print.

Sublimated garments contain the most aggressive sublimation dyes. Blocker Gray provides excellent blocking for most sublimated garments. For the most extreme cases, use Blocker Black LG for maximum blocking density.

I need a blocker that works at high mesh for detailed designs on polyester.

Blocker Gray prints through mesh up to 305/inch — the same range as 301C Clear. You can print detailed blocker underbases at high mesh without sacrificing blocking performance.

My blocker keeps drying in the screen during production.

Add Retarder MG at 1–5% to extend open time. Browse all Matsui additives here.

Matsui Under Base Blocker 301 Gray Key Features

• Stops dye sublimation migration — carbon-based barrier prevents polyester garment dyes from migrating into and discoloring your ink layers
• Works under both water-based and plastisol inks — use it under your Matsui water-based system or under plastisol for softer prints
• Softer than plastisol blockers — water-based acrylic formula cures to a thinner, more flexible barrier
• Neutral gray underbase — excellent dye blocking without the heavy visual influence of a pure black underbase
• High mesh capability — prints through 110–305/inch for detailed blocker underbases or bold coverage
• High opacity with fast flashing — provides a solid foundation for bright top colors
• Ready-to-use or DIY — buy premixed Gray or mix your own with 90% Blocker Black LG and 10% Stretch White
• Compatible with all Matsui acrylic bases and whites — works under 301C Clear, Stretch Clear, EasyPrint Clear, all whites, and all Neo Pigment colors
• PVC-free and eco-compliant — OEKO-TEX® Standard 100, CPSIA, and HR4040 compliant
• Zero viscosity modifications required — prints from the container