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++Flexible Open-Cell Foam


























































































Northstar Polymers, LLC

3444 Dight Avenue So.

Minneapolis, MN 55406

Tel: 612.721.2911

Fax: 612.721.1009

E-Mail: info@northstarpolymers.com












Northstar Polymers, LLC is a member of Polyurethane Manufacturers Association.


Copy right reserved by Northstar Polymers, LLC 2000 - 2007.  Northstar Polymer prohibits duplication of the contents of this web site for the purposes of public display and/or using on another web site without a written authorization by Northstar Polymers, LLC.




Hand-Mixable Flexible Foam

6-pounds-per-cubic-foot density


This foam formulation is designed to make molded flexible foam parts/sheets/dies/blocks by hand-mixing or by the meter dispensing equipment.  The components are stable liquid at room temperature and ambient pressure.  It requires minimum tooling for a small production or short runs.  These properties are ideal in small scale productions for custom foam applications such as custom seating, padding, and cushioning.  Generally, lower density grade foams are softer than higher density foams.  For firmer foam quality, our 8 pound-per-cubic foot formula MPS-F08A or our firm-flexible grade foam formula FFM-1 is recommended.


The free-rise density of the foam is 5.5 pounds per cubic foot, and the cell structure is designed to be open-cell.  This is an MDI base water-blown polyester/polyether hybrid system, and it does not use flammable or ozone-layer-depleting auxiliary blowing agents



Examples for Applications:


  • Molded Upholstery Parts

  • Custom Seating, Padding, and Cushioning Parts

  • Custom Packaging of Impact/Vibration-Sensitive Items

  • Prototyping



Physical Properties of the Cured Foam



Property Tested


Foam Density (Free Rise)

5.5 LBS/Cuft

Typical Compression Density

6.1 LBS/Cuft

Compression Deflection (25%)

1.7 psi

Compression Deflection (50%)

4.0 psi

Bashore Rebound


Tensile Strength

38 psi

Tensile Elongation

121 %

Split Tear Resistance

3.7 pli

Apparent Surface Hardness

Shore OO 28 – 33


The above data is typical properties of the 6.1 LBS/cuft compression foam based on our in-house test methods.



The data is based on result of our in-house test method on 6.1 pounds per cubic foot density compression-molded samples at 1” thickness. 


Component Properties

                                                Prepolymer (Part-A)       Curing Agent (Part-B)

Code Number:                           MSA-018                       PPB-027                      

Specific Gravity:                         1.183                            1.024   

Equivalent Weight:                     183                               274                              

            %NCO                              23 %                             n/a                               



Mixing Ratio                             (Part-A)                       (Part-B)


Volume Ratio:                           1.00                              1.75

Weight Ratio:                            1.00                              1.49

Stoichiometry:                           1.000                            0.99

NCO Index                                 1.009                            1.00


Processing Temperature:


Part-A                                       Ambient

Part-B                                       Ambient

Mold/Substrate                        100 - 130 ºF


* The ideal temperature for the mold and substrate is 100 - 130 ºF. However, if you are using plastic mold, this may not be necessary.  For all metal molds, the temperature needs to be between 100 to 130 ºF. 


Cure Pattern:


Pot life (pour within)                    20 - 25 seconds

Demolding time                          20 - 40 minutes

Complete Cure Cycle:                24 hours at room temperature


(The surface of open-cast foam remains tacky for several hours at room temperature.  Post-curing in an oven at 180 °F temperature for 1 hour can remove tackiness quicker.)


Recommended Processing:


We recommend testing small amounts to see how the material behaves, then develop your processing method accordingly.  In here, the descriptions are for the manual hand-mixing process.  When you process/test, please be sure to operate in a well-ventilated area or large open area, wear rubber gloves, long sleeves, and protective eyeglasses to avoid skin/eye contact. Read the enclosed Material Safety Data Sheet for details on the safety and handling.


-          Before you start your test, there is a chance the part-A material being frozen during the transportation in the cold seasons.  Freezing causes phase separation within the components.  In such case, you need to heat the part-A component to 140 – 160 °F to thaw and agitate the content by rolling the container(s).  Do not open the container for part-A (MSA-018) until you are ready to use as it is a moisture sensitive material.  Do not use a wooden paint stick as it contains moisture which contaminates the material.  After agitating the component, keep them at a room temperature above 70 ºF.  The material is most stable at room temperature between 70 °F and 90 °F.  Storing the components at a higher temperature accelerate deterioration of the quality.


-          Pre-heat the mold and/or substrate to between 100 and 130 ºF. 


-          Apply mold release into the mold.  Do not use mold release containing a high concentration of silicone as it may destroy the foam surface.


-          Calculate the total inside volume inside the mold (or the finished part volume) in cubic feet.  Multiply it by the free rise density. This will give you the weight of the component mixture at the free-rise density in pounds.  Add 5 to 10 % for compression molding.  (See below for more detailed information on compression molding).  This will give you the total weight for the two components. 


-          Take the correct ratio of part-A and part-B into a mixing cup.  Mix well with a steel or plastic stir stick for about 20 seconds.  Agitate vigorously and thoroughly.  Scrape the material off the side and bottom of the cup as you mix.


The pot life for this foam formulation is limited, thus there is a limit to the quantity you can mix well manually by hands.  Employing a meter mixing/casting machine may be best for your production if your part is large or your production quantity is high.


-          Cast the mixture into the mold.  The mold should be between 100 and 130 ºF.  You may use ambient temperature if you are using plastic mold that does not absorb heat so much.  If your mold is of metal or other heat-absorbing material, the material may not cure properly under the room temperature.  Excess heating also affects the foam quality. 


-          Cure the foam in a mold for at least 20 to 40 minutes before demolding.  Check the strength of the foam surface before demolding.  The surface of the foam may be fragile at this point.  The open top surface may still be tacky, but this is normal.  The tackiness should disappear when the foam is cured completely.  


-          The foam should be open-cell structured if you are simply open casting to make block, die, or sheets.  However, if you modify mixing ratio or molding it in a compression mold, the cells in the foam may not be sufficiently opened.  If the cells in the foam are not opened, this will lead to substantial shrinkage after the foam is cooled.  Compress the foam with hands to test to see if the foam has an open-cell structure while foam is warm.  If it feels like balloon that bounces back strongly as you press farther, the foam cells are not opened.  In such cases, physically crush the foam by hands and try to pop the unopened cells in the foam.  This will prevent shrinking of the foam by cooling.  (All flexible foams shrink slightly.  Design your mold accordingly if tighter dimensions are required. The expected linear shrinkage is 4 to 10% for compression-molded parts.  Higher processing temperature causes higher shrinkage rate.)


-          Store at room temperature for 24 hours to complete the cure cycle before evaluation.


Compression Molding


Foam needs to fill the mold space by put slightly larger amount of foam into the mold.  The expansion pressure of the foam sends the foam material to fill the mold to the expected shape.  The mold, therefore, needs to be a closed mold and has to have a capacity to retain the internal pressure.  A simplest compression mold will be an open-top box with a lid.  The lid needs to be clamped to hold the pressure. 


The air trapped in the mold could make large voids if it is not vented.  For this purpose, you need to have very small holes to let the trapped air escape from the mold.  Determine the mold position so that trap air is pushed toward a corner or sections where the vent holes are.  Small amounts of the foam may squeeze out from the vent holes, which you can machine off after the part is cured.


The mold material can be metal, plastic, or elastomeric material.  Mold surface needs to be slick as foam could stick to any porous surface.  Metal molds tend to absorb heat.  The heat created from urethane reaction is required for foam to cure properly.  If mold is cold, this heat is absorbed and the foam does not cure properly.  The mold needs to be heat to 100 to 130 ºF range in case of using metal molds.  If your mold is made of a plastic or elastomeric material, such as silicone rubber, epoxy, and urethane, this may not be necessary.  Please test and determine the optimal temperature for your mold.  Higher mold temperature increases the shrinkage rate.  For tight shrinkage variation, controlling temperature parameters is very important. 


The “compression rate” describes the additional amount of material you would put into the closed mold to create the internal pressure so that the foam fills the entire inside space of the mold.  Typically, about 5 to10 % compression should give enough pressure to distribute the foam within the mold.  Using higher rate makes the foam denser and stronger.  However, it will increase the chance of closed-cell/shrinkage problem described below. 


Trouble Shooting


- Shrinking Problem from Closed-Cell Structure


This material uses a chemical reaction within the formulation to create CO2 (carbon dioxide) gas as a source of foaming.  This reaction happens when the material is hot, so this gas is hot when foam is made. As the foam cools after curing, CO2 gas also cools; as it cools, the volume of gas contracts.  If the cells in the foam are not opened, this CO2 gas takes the whole foam down and shrinks the foam significantly.  It would look like a prune.


To avoid this, you need to make an open-cell foam structure.  This specific foam at the specified mixing ratio, the foam should have open-cell structure when it is open-cast to make free-risen foam.  However, by compression-molding, it increases the wall strength of the foam cells, and this may prevent the cell from opening.  This often happens when the compression rate is high or processed at an elevated temperature.  When this happens, the foam quality becomes “balloon-like” soon after it foamed while the foam is warm.  If possible, crush this foam at about 30 – 40 minute point while the foam is still warm. You will hear popping sounds from the foam as you crush.  You can keep crushing until you hear no more popping sound.  This will open the cell inside of foam and will prevent the large shrinking.  The foam also should feel significantly softer when you compress.


- Preventing Air Voids by Vent Holes


When you compression-mold a foam product, air inside the mold must be vented as the foam rises.  Other wise you would trap the air at the corners and it makes large voids.  Your compression mold must have vent holes.  (Sometimes, this is erroneously thought that there is not enough material in the mold.  Increasing the amount of material does not solve this issue.)


You need to develop a parameter for where in the mold the material should be placed, and how the mold should be positioned while foam is expanding in the mold.  This will determine where the air in the mold is pushed when the foam expands.


When you find the pattern for the air void(s), you would need to put small holes to where the voids form so you can release the in-mold air.  The vent holes should be small enough so that they will be closed with the foam after the air is pushed out, so you will still have the internal pressure.  After the part is demolded, you may need to machine off the small amount of material squeezing out from the vent holes.  


- Inconsistent/Large Foam Cells


If you see many small voids in the foam, this may be because the material is cast in while the mixture is creaming and loosing its flow.  You may be enclosing more air into the foam while the mixed liquid has a high viscosity.  You may need to finish agitating earlier to avoid enclosing too much air.


Another possible cause is that the material may be touching the side wall before it is dropped to the proper position for the material to be placed in the mold.  The material on the side wall starts to foam before the expanding foam from the bottom reaches there.  The foam material stuck on the side wall blocks the passage, which can cause voids.  Place the mold in such position that you can pour the material to the bottom without touching the side wall of the mold.


If you see inconsistent foam cells near the mold surface, your mold release may be affecting the quality.  Try using different mold release.  Silicone and a few other mold release constituents can affect the surface tension of foam material, which may destroy the cell structure.  Also, if the mold temperature is too high, it would affect the cell structure near the mold surface.  Try at lower mold temperature.



Other Information


Applications that requires fire-retardant property:


This foam is not fire-retardant foam, and it is not recommended for applications, which require or should be using fire-retardant grade materials.  The applications such as automotive interior, building material, and components for some electronic parts often require fire-retardant grade materials by law. It is the user's responsibility to conform to the applicable regulations.  We also do not recommend this foam to be used to the applications in which the foam can be exposed to high temperature or being near an ignition source.


By adding fire retardant additives, this foam may be modified to fire-retardant grade foam.  The user must test the foam modified with the fire retardant additives for the fire-retardant property and the conformance to the applicable regulations.




Part-A component (prepolymer) contains isocyanate component, which is very much sensitive to moisture.  If it is left in air, part-A will react with atmospheric moisture and will be ruined.  This reaction is non-reversible.  Soon after opening a can and dispensing the content, nitrogen gas or argon gas needs to be injected to the can to blanket the material.  Silica gel or calcium chloride desiccant filter should be installed to 55 gallon drum-vent for your drum feeding system.  The storage temperature should be at a room temperature between 70 and 90 ºF.


Part-B component is hygroscopic.  If the material is exposed to ambient air, it may absorb moisture. Moisture contaminated part-B material may become source of degradation or excessive bubbles in the product. Avoid exposure of the material to air.  Purging the empty space in the container with nitrogen gas or negative-40-degree-due-point dry air is also recommended to prevent moisture contamination of part-B as well. The storage temperature should be at a room temperature between 65 and 90 ºF.




The component materials are industrial-grade chemicals.  Please keep them in a secure place and prevent access from any unauthorized individual.  The personnel who handle these materials need to read the Material Safety Data Sheet (MSDS) for detail information on safety and handling of the material.  The MSDS for each component is sent with the shipment of the material. 


Whenever using this material, please be sure to operate in a wide-open area with good air movement or in a well-ventilated area. Wear rubber gloves, long sleeves, and protective eyeglasses to prevent skin/eye contact of the material.  When your operation involves heating or spraying of the material, we recommend, in addition to the above, installation of a proper ventilation system and using a half-face respirator recommended for the use to prevent inhalation of the fume.  


Direct contact of polyurethane raw materials to skin/eye, as well as ingestion may lead to health problems.  No eating or smoking should be permitted at the working area.  The operator should wash hands well with soap and water after handling the materials.  Please refer to the MSDS for each component for the detailed health information.


For any questions, please contact Northstar Polymers.


Tel:          612-721-2911.

Fax:          612-721-1009

Web Site:     http://www.northstarpolymers.com

E-Mail:       info@northstarpolymers.com


Notice: All of the statements, recommendations, suggestions, and data concerning the subject material are based on our laboratory results, and although we believe the same to be reliable, we expressly do not represent, warrant, or guarantee the accuracy, completeness, or reliability of same, or the material or the results to be obtained from the use thereof, neither do we warrant that any such use, either alone or in combination with other materials, shall be free of the rightful claim of any third party by way of INFRINGEMENT or the like, and NORTHSTAR POLYMERS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, OF MERCHANTABILITY and FITNESS FOR A PARTICULAR PURPOSE.


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Northstar Polymers, LLC

3444 Dight Avenue South

Minneapolis, MN 55406

Tel: 612.721.2911

E-Mail: info@northstarpolymers.com


Notice: All of the statements, recommendations, suggestions, and data concerning the subject material are based on our laboratory results, and although we believe the same to be reliable, we expressly do not represent, warrant, or guarantee the accuracy, completeness, or reliability of same, or the material or the results to be obtained from the use thereof, neither do we warrant that any such use, either alone or in combination with other materials, shall be free of the rightful claim of any third party by way of INFRINGEMENT or the like, and NORTHSTAR POLYMERS DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, OF MERCHANTABILITY and FITNESS FOR A PARTICULAR PURPOSE.