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Cold vs Hot Latex

David BoccabellaDavid Boccabella Brisbane, Australia Moderator
Hi Folks.
Just keeping my ear to the industry beat.   
Hot Foam Latex (oven cure) is nice, light weight, can be painted and hair punched.

Whats the closest effect re using either a silicone foaming/ Urethane foam/ Something Else that one can get without having to use an oven.

Many thanks


  • Chris EllerbyChris Ellerby Los Angeles Admin
    Polyurethane foam might be the closest, though it is not as flexible as foam latex.  I've yet to try anything with silicone foams, but that would be a lot of fun to play with!

  • Foam latex can cure at room temperature. And, the resulting foam is fantastic. BUT, IT WILL TAKE AN EXTREMELY LONG TIME TO CURE!!! The reason foam latex is usually baked, is to greatly speed up the cure time. When foaming, it releases strong concentrations of ammonia. Which, of course, needs proper ventilation. And, if foam latex is overcooked/overcured, it will usually tend to stink like flatulence, (ammonium sulfate). With the right amount of foaming with special additives, you can achieve variable volumes/densities from x2, to x8. Or, in some instances, you can achieve super high volumes/densities near x10 to x15! The best temperature range to bake foam latex is between 120-150 degrees F. If you have any kind of latex allergy, avoid foam latex like it is the plague! No mould release can be used in resin-based moulds, (it helps, but it is not entirely needed, per say.) Stone-based moulds should have mould release. All standard mould releases should work for foam latex. If at all possible, avoid ordering during the winter months. If it freezes, it will become completely useless!

    Flexible polyurethane foam, (a.k.a. "cold foam), can result in an extremely soft, to very firm end product, depending on density. The lower the density, the higher the volume. You can find polyfoams that can increase in densities, from 2-4lb. density, to as high as 20lb. density. Of all the different foams available, these are usually the cheapest. But, it tends to have very poor tear strength. And, the fumes it releases while foaming & curing are quite toxic, (they are "Isocyanates", which can be leathal in high concentrations.) Prolonged, repeated exposure to the uncured components can lead to chemical sensitivity, and irritation. If you use it, MAKE SURE YOU USE PLENTY OF PROPER VENTILATION! The final cured foam(s) are relatively safe. But, some folks can still have VERY bad allergic reactions to it. It can be easily painted with most the same paints foam latex can. And, in most cases, this foam will require mould release. ("S.C. Johnson Paste Wax", dissolved in 99% isopropyl alcohol, makes a surprisingly good, & cheap release, that can be used with polyurethane foams, AND foam latex. Make sure the mould release is thoroughly dry before casting.) These foams can usually be ordered during winter months without much difficulty. Check with your supplier(s) about specific brands.

    Silicone foam, is actually pretty safe, comparibly speaking. You should use, (you guessed it), proper ventilation, (as is cures, it releases carbon-dioxide, which isn't healthy, but it won't kill you immediately). It does have some strong caveats of it's own, though. It is "Platinum-cure" based, which means it is VERY SENSITIVE to sulfur & other contaminants. Most silicone foams only increase in volume x2, Which means this foam will also be quite heavy, compared to most other foams. It can be torn relatively easily. It usually will foam up EXTREMELY FAST! So, you will need to work as quickly as possible to mix it, and get it into the mould(s). And finally, it is very expensive. Resin-based moulds can be used without release, (but, using release will still help in removal of castings). Stone moulds definately should use release. An inexpensive, yet effective mould release for silicone foam as well as most silicones, is regular, old-fashioned dish detergent. This should be mixed 1:1, with 99% isopropyl alcohol. this solution may be brushed or sprayed into you mould(s), and left to dry thoroughly. 2-3 coats applied should be enough. Make sure it is completely dry before pouring the silicone foam. Once the foam is cured, it is easy to rinse any mould release residue away with water. Silicone sticks best to silicone. So, for best results, paint any silicone foam castings with... (surprise!), silicone! Again, these foams can usually be ordered during winter months without much difficulty. Check with your supplier(s) about specific brands.

    Nearly all regular materials we use tend to work best if used at a room temperature of around 70-80 degrees F. Higher heat may shorten "pot-life" & cure-times. And, colder temp.s may extend them. While every material has it's own set of good & bad points, it really comes down to personal preference which one you decide to choose.

    Hopefully, this information will help some, (and, didn't cause information overload).

    Good luck.
    -Jeffrey warren Park
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