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Old Dec 14, 2012, 10:51 AM
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United States, MA, Boston
Joined Oct 2010
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Question
Best Foam for Filling and Building

I realize this may seem like a simple question, but for some reason I can't seem to hunt down a finite answer.

I'm doing a project that require some ares of a balsa, built up model to be filled or shaped out of foam. I'm wondering:

1. What is the best kind of foam for light weight, strong, and easy shaping?

2. Where can I buy it (Home Depot, or rc store)?

3. Can I put iron on covering on it without worrying about melting it?

Thanks
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Old Dec 14, 2012, 11:41 AM
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Staffs, UK
Joined Nov 2003
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I generally use Dow Floormate, commonly known as "blue foam". It's easy to shape and reasonably light. Whether it's strong enough depends on what you're intending to use it for. It doesn't like very high heat so Monocote might be tricky but lower temp films like Ultracote, or over here Solarfilm, are usually o.k.

No idea where you can buy it in your part of the world, sorry.

Steve
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Old Dec 14, 2012, 12:58 PM
B for Bruce
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The 'Wack, BC, Canada
Joined Oct 2002
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The blue or pink expanded polystyrene foam is the best choice without getting involved with specialty foams. You can buy it easily at any of the larger lumber and hardware yards like Home Depot or Lowes.

It does not like heat though. It's best to stretch a heat shrink covering over it and stick it just around the edges onto the wood. Or you could try insulating it from the heat of the covering iron by applying a layer of 4 oz glass cloth to the foam using some sort of light adhesive like a spray glue or even common glue stick. You don't need to use resin since the idea is that the cloth would be strictly a bit of an insulative separator between the foam and the heat used to shrink the plastic covering. You'd still want to only stick the covering firmly to the wood around the edges and not to the foam or cloth layer. And when you shrink the foam get onto it and back off FAST. Don't fuss about with it or the heat will extend down through the glass cloth and insulative air and get to the foam. If there's a wrinkle or two that needs extra attention let things cool off first then go at it again for a few more seconds.

Another option would be the foam used for dry and fake flower arrangements. I've never worked with this foam but I know you can get it in blocks and other shapes from craft stores such as Micheal's. You'd need to get a bit and try it out to see if it's as heat sensitive as the extruded polystyrene stuff.
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Old Dec 14, 2012, 01:47 PM
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Thanks Bruce and Steve. I expected the standard insulating foam was the way to go, but did not know about the heat concerns. Glad to have learned about it before I was putting the finishing touches on a plane.
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Old Dec 14, 2012, 03:17 PM
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Another option would be the foam used for dry and fake flower arrangements. I've never worked with this foam but I know you can get it in blocks and other shapes from craft stores such as Micheal's. You'd need to get a bit and try it out to see if it's as heat sensitive as the extruded polystyrene stuff.
Don't try it.The stuff has zero strength,you can literally push your finger in to it.
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Old Dec 14, 2012, 10:42 PM
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The 'Wack, BC, Canada
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Quote:
Originally Posted by Stupot46 View Post
Don't try it.The stuff has zero strength,you can literally push your finger in to it.
Well, yeah. But the same is true of the blue and pink stuff. At least to the extent that if you don't exercise some restraint in handling the final products that you'll leave dents in the surface.

But you do raise a valid point. And it suggests that actually applying some form of glue or other "resin" to some smoothed over fiberglass cloth done to insulate the foam might not be a totally bad option. The skin thus created could provide the sort of strength needed to avoid damage due to handling incidents.
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Old Dec 15, 2012, 12:31 AM
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United States, MN, Hermantown
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I really like the Owens-Coring Foamular 250. (pink) Yes, it may dent, but you would be hard pressed to put your finger thru it. You might break your finger first. Great to carve or hot wire, easy to sand. You can take it down with 60-80 grit to start, and a 220 grit will give a nice smooth finish

If you hold a heat gun directly on it, it will deform. Never tried it with a covering, only have fiberglassed it. depending on the store, you may have to buy a full sheet. 4'x8' thicknees will vary by store

Should be plenty of Home Depots on the east coast.
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