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Last-A-Foam vs Divinycell

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GESchwarz

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Oct 23, 2007
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I'm trying to learn about the differences between Last-A-Foam and Divinycell foam.

I understand that Divinycell is used as a rib material in some European kitplane designs. It is PVC. Cost versus thickness is exponential.

I understand that Last-A-Foam is unaffected by water, fuels, and most solvents. It is a Polyether Polyurethane. Cost versus thickness is linear. Temperature resistant beyond 200 degrees F. It's flexible varieties are used as a shock absorbing material...I'm considering using about 10" to 12" of this as a seat bottom to save my spine, topped with Confor Foam Seat Cushion. Is flame retardant.

Strength Comparisons between the two materials shows that Divinycell is about 2 times stronger than Last-A-Foam for the same density. Analysis shows that strength of Last-A-Foam is proportional to density, so increasing density by 2 times gets you to an equivalent strength of Divinycell. This 2 times figure is an average of Shear, Tensile, and Compression. The Last-A-Foam of twice the density is actually about 1.5 times the strength of Divinycell in Shear and Compression, and about .84 times the strength in Tensile.

Both are used in sandwich construction. Both are used in fiberglass boat hull construction. Both are closed-cell and thus prevent liquid intrusion.

I just did a price comparison of the two material densities that would yield the 2x density as described above. 3 lb/sqft of the Divinycell versus the 6 lb density of the other, both in 3/4 thickness worked out to about the same price at $5.34 and $5.62/sqft respectivly. So at that thickness, Divinycell is the greater value because it is half the weight.

I am soliciting further light and knowledge on this subject if there are any among you who are experienced in either, or both of these materials.
 
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GESchwarz

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Thanks Dave, I should have done that at the begining. I've just learned that Divinycell is popular with surfboard manufacturers.

...A result of searching through this forum has revealed that Orion has observed that the Last-A-Foam may have a fraibility issue and can fail in the presence of vibration over time. He indicated that it may not be a true "closed cell" structure; closed cell is superior to open cell with respect to strength and liquid intrusion.
 
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orion

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I remember many, many years ago making a plug out of L-a-F and as I tried to remove it, fist with chemicals, all it did was get heavier. Closed cell? Not quite. And yes, tends to fail in very brittle fashion.
 

wsimpso1

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Saline Michigan
Friends don't let friends build with Last-A-Foam. I have had a bad experience with LAF that is in the forums too. My entire bird is either PVC cores or hotwired styrene foam. Use PVC for your cores and be happy.

I don't get your "cost is exponential with thickness" comment. The stuff is cast in huge blocks and panels are sawed from it. If your supplier is really charging much more (per pound) for for one thickness over another, search out some other suppliers.

Billski
 
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