The HydroSpan 400 product was invented by Industrial Polymers for reducing the size of 3-dimensional objects while maintaining high surface detail. The HydroSpan 400 product is a urethane resin which quickly cures when mixed with ordinary tap water. We recommend using COLD water (ice cold water) to extend the very short working life of this product. You must create a mold of the original object you which to shrink in size and then fill the mold with HydroSpan 400. The HydroSpan 400 will rapidly cure in your mold within minutes. Remove the HydroSpan 400 casting from your mold and place in a low humidity environment to begin the reduction process. You have only 1 to 2 minutes to pour this material into your mold after mixing with COLD water before it cures. See the video demonstration below. The amount of water used in the reaction depends on the amount of reduction you wish to achieve.



The HydroSpan 400 shrinks proportionally as water evaporates out of the cured product. You may use a food dehydrator to speed the shrinkage process or simply leave the casting in a low humidity environment for it to shrink; it produces very accurate reductions of any casting. Most of our experience with this product has been with shrinking objects with a starting size of approximately 6 inches in diameter. Very large castings may be more difficult to shrink because it will take much longer for the water to evaporate from the HydroSpan 400 casting. You must monitor the shrinking process until the desired size is achieved. When the desired reduction size has been achieved you will make your new production mold from the reduced HydroSpan 400 casting. You may use molds made from urethane rubber, silicone rubber, metal or plastic to cast HydroSpan 400. Silicone spray mold release or wax based release agent must be used to prevent sticking of HydroSpan in your mold, except for silicone rubber molds which are naturally releasing.

HydroSpan 400 is a unique single component, Flexible, 100% solids (contains no V.O.C.), polyurethane elastomeric compound. HydroSpan 400, when fully cured provides for a simple method for reducing three-dimensionally molded parts. Reduction of parts is done by simply molding the part with HydroSpan 400 to form a rubber master. After curing 30 minutes at room temperature the molded HydroSpan 400 part is removed from the mold and allowed to shrink at room temperature. Reductions from 55 % to 86% the original part can be made depending on how much water is added in the initial curing process. Full reduction of parts can be achieved in 5 to 14 days depending on cross section thickness of the part. Thicker cross sections take longer while thinner cross-sections require less time.

Application and Mix Ratio

Mix HydroSpan 400 with COLD water (40˚F-50˚F) to extend working life. See Polymer/water mixing chart to determine the amount of water to use to achieve a specific reduction. Use a maximum batch size of no more than one gallon total mix of HydroSpan 400/Water.

Pour both the water and HydroSpan 400 into a clean plastic container and quickly mix using a spatula for batch sizes of a ½ gallon or less or less mix by hand with a flat spatula, for larger mixes use a jiffy mixer and electric drill. Take care to scrape the bottom of the container to include all of the unmixed HydroSpan 400 polymer (do not use square or round rod as mixers). Mix for about 30 seconds and quickly pour into the prepared mold. After about 3 to 5 minutes HydroSpan 400 cures to a firm white gel.

Mold preparation HydroSpan 400 can be molded in almost any kind of mold as long as it is fully prepared before filling with the uncured polymer. Release agents used in the molding process inhibit the evaporation of water thus slow down the reduction process of the part. Depending on relative humidity and temperature, parts can be handled in 30 minutes.

Reduced Parts Once the HydroSpan 400 parts have reduced to the desired size a final mold should be made as soon as possible. If molds are made from flexible RTV urethane or silicone rubber a light layer of Vaseline petroleum jelly should be applied to prevent any unwanted reaction of the absorbed water in the HydroSpan 400.

Reduced HydroSpan 400 parts maintain their reduced size if stored in a dry environment.

Water Curing Solution by Weight


HydroSpan 400 resin/water solution

Gel Time

Size of the finished part
Compared to Master (100%)

 1 part / 2 parts

 1 min 10 sec


1 part / 3 parts

1 min 15 sec


1 part / 4 parts

1 min 15 sec


 1 part / 5 parts

 1 min 15 sec


1 part / 6 parts

1 min 20 sec


1 part / 7 parts

1 min 19 sec


1 part / 8 parts

1 min 30 sec





Physical Properties




Working Life @ 72°F

3-5 minutes

Specific Gravity:



8.95 lbs.


Clean Up

Dispose of all empty HydroSpan 400 component containers in accordance with local, state and federal regulations. Empty component containers can be rendered non-hazardous by rinsing the containers with a small amount of mixed material and allowing the solvents to evaporate. The containers will then contain non-hazardous cured urethane.

Storage and Shelf Life

The containers should be stored in a cool dry area that is protected from direct sunlight and moisture. Storage temperatures should not exceed 80°F. The shelf life of factory sealed containers stored under these conditions is six months.


Shipping Class: Class 55 Non-hazardous