Matsui Under Base Blocker 301 Gray | Water-Based Dye Migration Blocker for Polyester, Performance Fabrics & Sublimation-Prone Garments — Works Under Water-Based AND Plastisol Inks

Matsui Under Base Blocker Technical Data Sheet

Matsui Under Base Blocker Safety Data Sheet

What does Under Base Blocker 301 Gray do?

It stops dye sublimation migration — the process where polyester garment dyes re-gasify under heat and migrate upward into your ink, discoloring your print. Blocker Gray is printed as the first layer, directly on the garment, before whites and colors. It creates a barrier that prevents garment dyes from reaching your ink layers.

Can I use Blocker Gray under plastisol inks?

Yes — this is one of the most valuable features. Print Matsui Blocker Gray first, flash at 320°F, 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 stack is noticeably softer. You do not need to change your plastisol color system. Just change the blocker layer.

What is the difference between Blocker Gray and Blocker Black LG?

Both stop dye migration. Blocker Gray is premixed gray — it provides excellent blocking with a neutral underbase that does not darken lighter top colors. Blocker Black LG is pure black — it provides maximum blocking density for the most aggressive bleeders but can darken the appearance of lighter top colors. Most shops stock Gray for daily use and Black LG for problem garments.

Which garments need a blocker?

100% polyester, especially dark and bright colors, poly blends with 50% or more polyester, performance Dri-Fit fabrics, sublimated garments, and camo patterns on polyester all need a blocker. 100% cotton typically does not need one. 50/50 blends and dark tri-blends should be tested. When in doubt, test — dye migration can take up to 72 hours to fully show up.

Why does dye migration sometimes appear the next day instead of immediately?

Sublimation dyes re-gasify when heated. Residual heat energy in the garment can continue driving dye migration for 24–72 hours after printing. A print that looks perfect at 1 hour can show bleed at 48 hours. Always test 48 hours out before confirming a production run on a new polyester garment.

Can I make my own Blocker Gray?

Yes — blend 90% Blocker Black LG + 10% Matsui Stretch White. This gives you the same premixed Gray you get from the container. Shops that already stock Blocker Black LG and Stretch White can mix their own to avoid stocking a third product.

What mesh count should I use?

110–305/inch. For maximum blocking coverage on aggressive bleeders, use 110–156 mesh with a thicker stencil for a heavier deposit. For standard polyester work, 156–200 mesh. For detailed blocker underbases, up to 305 mesh — but heavier deposits provide better blocking performance.

Does Blocker Gray work on sublimated garments?

Yes — sublimated garments contain aggressive sublimation dyes, and Blocker Gray provides excellent blocking for most sublimated garments. For the most extreme sublimation dye migration, use Blocker Black LG for maximum density. Always test before production.

Is there a blocker for the 350 Series polyurethane inks?

Yes — the 350 Series uses its own Under Base Blocker 350, not the 301 Gray or 301-LG Black. The 301 blockers are for the acrylic system and for plastisol compatibility.

What about Kombat Blocker?

Kombat Blocker is another Matsui blocker option designed for polyester dye sublimation control. Consult with your Matsui representative or test both to determine which provides the best results on your specific garment brand and dye chemistry.

Can Blocker Gray be dry cleaned and ironed?

Yes — prints made with Blocker Gray can be safely dry cleaned and ironed without compromising the blocking performance.

Is Blocker Gray safe for children’s clothing?

Yes. Blocker Gray is OEKO-TEX® Standard 100 certified, suitable for baby products, CPSIA compliant, and HR4040 compliant. It is PVC-free and environmentally safe.

Why is the hand feel softer with Matsui Blocker Gray under plastisol than with a plastisol blocker under plastisol?

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-based plastisol. With Matsui Blocker Gray, that heavy layer is soft, flexible, water-based acrylic. The plastisol color layers on top are the same in both cases, but the foundation underneath is dramatically softer with the water-based blocker. The cumulative result is a noticeably more flexible, more comfortable print.