Fill-It and Fill-It HTR are sulfur free clays used by mold makers to seal mold boxes, build dams, set parting lines/shims and repair cracks. They are both off white with excellent adhesive and feathering characteristics. They both are also very flexible and will not dry or crack.

Fill-It is softer than Fill-It HTR making it easier to handle at lower temperatures. Fill-It HTR is firmer than Fill-It and is less sticky at higher temperatures. The smallest amount of heat, just friction from rubbing it in your hands, will soften both products.

Both Fill-It and Fill-It HTR are packaged as one pound blocks, which are scored so that they can be broken into quarter pound sticks.

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Unique Properties

Both clays adhere well to a variety of materials including aluminum, polypropylene forms, a variety of foams, cardboard and paper. Fill-It products will not oxidize and can be left out or heated and cooled repeatedly without any significant change in the product.

Softening Temperature

Fill-It 100°F / 38°C
Fill-It – HM 115°F / 46°C


Wash hands with soap and water after use.

Handling Tips

Using small amounts of citrus-based solvents, lighter fluid, latex paint removers, turpentine or mineral spirits as a lubricant on the surface of the clay will help to attain a smooth surface. 


Heat over 90°F / 32°C will cause the original Fill-It to get very soft and sticky and the clay will begin to sweat or sag. The HM formula will tolerate these normal changes.

Fill-It™ Technical Bulletin (pdf)
Fill-It™ Safety Data Sheet (pdf)