Are Balsa Foam and "yellow foam" similar?

I was just wondering because we are going to do some final models soon in class and i’d like some options as for using harder denser foams that will look good. We are using the Blue insulation foam for mock ups, but I haven’t used Balsa or the “yellow” polyurethane foam I have seen some students use here at school. There is also Ren-shape… how does that compare to Balsa?

Thanks guys

40 views and no replies? :frowning: I guess the ones viewing this post must be also curious too about the differences between the two materials, if any?

I’m unfamiliar with “Balsa” foam.

I know of Polyurethane foam that I used back in school. Medium/Hard density. Pale yellow color with pinpoint sized holes throughout.

Is that what you’re referring to?

Ren is going to be much harder, at least 80 grit sandpaper for shaping by hand, if not CNC mill or mechanical sanders.

The Polyurethane foam I mentioned is much easier to work with but is less durable than the Ren.

The Ren is stronger and sturdier, so it can take more abuse, if it were to be used as a “functional” model.

Best image I could find of the Polyurethane foam

I found these images of Balsa foam… looks similar…?


Thanks for the reply! Well, I know for sure the yellow polyurethane one we use for sure here at school. It’s just that I had heard someone in class mention BalsaFoam and I looked it up and it looks like the yellow stuff, so wasnt sure if they were the same product, but with different names. I might stay away from Ren, if I want something easier to sand and work with, as you said. We do provide the Yellow foam here at school, but figured I’d find out what this Balsafoam was, in case i wanted to buy some online. Thanks again, Taylor.

one Pro about the Polyurethane foam is that you can order it in several different densities. I remember we had Low, Medium, High. High being the hardest of course. Low could be indented with your fingers.

however, on the Con side. it is extremely extremely bad for you. always wear a respirator, change your clothes after you’re finished (and wash them, don’t put them next to your bed to breath the dust in). I remember reading some really scary stuff about that foam, cancer being the least of your worries. Something about attacking your nervous system I believe.

That being said… the Balsa Foam (Balsafoam?) might be a great option or solution. From the images I saw of carvings and mini sculptures from the stuff I found on a google search, it looks pretty nice, works well, looks fairly durable, keeps its shape, nice detailing, etc. Call up a retailer or better yet, call up the factory themselves, and ask for a sample to be mailed to you… if they blow you up, call back and tell them you work for your college and you’re thinking about placing a large order for your department and you’d like a sample or two.

Good luck

If you can get the PU foam, I’d go with that instead of the Balsa. I used the balsa in school and it’s pretty much the same stuff, works and handles the same, easy to shape by hand, etc. But the balsa foam was more gritty and stuck to things more (table, hands, etc). You could never seem to really get rid of it. It has a weird tart/tangy smell and you can “taste” it as you work with it. I’ve found regular polyurethane to be more “inert”, you work with it, brush it off, sweep it up, no problem. Also metal tools that you use with the balsa foam would tend to rust really quickly, I believe they ended up banning it from our wood shop for a while because of what it did to the bandsaw blades.


Thanks for that info. Yes, I use a respirator even with the Blue Foam stuff. Other students in the process lab use Bondo and other harsh smelly stuff as well, so I never want to take chances with my lungs. I have heard ID professors of mine mention on more than one occasion being now asthmatic and/or having allergies that they didn’t have when they were students in ID decades ago and now are wishing they had protected themselves, so it’s enough to scare me to also take precautions. I think after reading what you wrote and also what Skinny mentioned about BalsaFoam, I will just stick to polyurethane. I have also read about BalsaFoam being detrimental to metal tools and would hate the process lab being mad at me for messing up their blades! :slight_smile:

Thanks Taylor and Skinny for taking time to respond to my post and answering my concerns.

When I was an intern about 12 years ago, the model shop banned one version of Balsa Foam because whenever it was left on a steel surface such as a table saw it would cause the surface to rust. My guess is that problem has been worked out. As far as densities of the foam, they are also rated in “pounds” 7 lb., 10lb, 12, 15, 20 and so on. For final cosmetic models try to get at least 12-15lb density. You can potentially build up layers of primer and not have to do any surface. The 7lb. density is too porrous and delicate.

oh god, whatever you do, stay away from Bondo!!!
that is some nasty stuff!!