The differences between EPS and EPP foam
Per request, here are some ways to tell the difference between EPS and EPP foam.
EPS stands for expanded polystyrene, otherwise know as styrofoam. Depron, fan fold foam, sturdiboard, and the blue and pink foams found at home centers, are all EPS. This foam is easy to cut, fairly easy to sand, fairly rigid, fairly brittle (cracks easily) and not very durable. If you press your fingernail into it, it will leave a permanent crease. If you hold a very small piece over a match, it will just collapse and dissappear. Regular CA glue will melt this foam, as will some types of spray adhesives and spray paints. Use foam safe CA on EPS foam. See this thread for glues that work on EPS:
EPP stands for expanded polypropylene. I know of no trades names for this foam other than EPP. This foam is more difficult to cut, very hard to sand, less rigid than EPS and much much more durable. If you press your fingernail into it, the dent will almost totally dissappear. If you hold a very small piece over a match, it will catch fire and burn. You can use any type of adhesive or paint on EPP, as long as it sticks. From my limited testing, polyurethane glues work the best on EPP, but epoxy, CA and many contact adhesives also work well.
I'll post some pictures of EPS and EPP a little later, or someone else can also post some pictures.
United States, CA, North Highlands
Joined Aug 2004
Here are two types of EPS.
Good old bead board /styrofoam AKA Expanded PolyStyrene, and
Bluecor / FFF AKA Extruded PolyStyrene.
Kind of hard to tell by looking at them that chemicaly these two samples are the same material.
Great info. from www.flyingfoam.com
Foam selection is dependent on the size of the model, type of covering, intended use and construction methods. Foam is produced in many densities, colors and types. Only a few types and densities are used in the modeling world.
Density is defined as the weight of 1 cubic foot of the material. In other words, a 12" x 12" x 12" cube of 1# density foam will weigh 1 pound. Higher density foams are harder to the touch and more rigid, but they weigh more.
The higher density foams are typically used in high aspect ratio wings that are relatively thin, like high performance thermal gliders. Powered pylon racers, even giant scale racers may also use 2# foam. Large models with thicker airfoil cross sections will work fine with 1# foam. The 1# foam is also used on most powered sport airplanes, trainers, and any airplane or glider where weight is a concern.
Types of Foam:
We stock a number of types of foam, and some types are available in different densities:
- 1.0# EPS
- 1.5# EPS
- 2.0# EPS
- Owens Corning Pink Foam (1.8# density)
- Dow Blue Square Edge (1.8# density)
- Dow Blue Hi-Load 40 (2.0# density)
- Surfboard Foam (AKA Spyderfoam, 2.3# density)
- 1.3# EPP
- 1.9# EPP
EPS - Expanded Polystyrene Foam:
The EPS foams that we use are white beaded foams that commonly used for insulation material or in architectural applications. White foam is available in any thickness up to 8 inches in 1#, 1.5# or 2# density. We purchase EPS foam in large billets, and slab cut it into sheets in our shop. By doing this we get a foam sheet that is flat, has a better surface finish, and a more uniform thickness than is typically available from insulation suppliers.
Blue / Pink Foam:
Blue and Pink foam is readily available in home improvement stores in many parts of the U.S., but not in Southern California. These foams are a higher density material that is typically used as cold weather insulation on basement walls and footers. In Southern California, we have neither basements nor cold weather, so Blue and Pink foams are not as readily available here.
We stock Dow Blue foam in 25 and 40 psi compression and Owens Corning Pink Foamular which is 25 psi compression.
These are closed cell extruded foams that have a finer grain than 2# white beaded foam, but the mechanical properties of the two are similar. We stock Blue foam in 2" thick sheets and Pink foam in 1 1/2" and 2" sheets. Blue foam is also available in 25psi compression in 3" and 4" thick sheets as special order items.
Surfboard foam is manufactured by Dow, and is a polystyrene foam similar in feel and texture to blue foam. The big difference is that surfboard foam has grain structure that runs vertically through the sheet. Because of the grain structure, it has a compression rating greater than 60 PSI, which is greater than other types of blue or pink foam. Spyderfoam density is 2.3 # per cubic foot.
EPP - Expanded Polyproplyene Foam:
EPP is flexible foam that is used as a packing material for delicate electronic parts. It is also used in the bumpers of some automobiles. It is a rubbery material that is light in weight, yet very durable.
EPP is available in 1.3# and 1.9# densities. EPP is used in the modeling world for combat gliders that need a high degree of durability. Since EPP is not a rigid foam, most all EPP gliders use fiberglass, carbon fiber, or spruce spars for stiffness.
Because of it's lack of rigidity and higher cost, EPP foam is not generally used in models that are covered with balsa, plywood, or obechi sheeting. EPP wings are typically covered with colored shipping tape, or low temperature heat shrink coverings like UltraCote. EPP is about 3 1/2 times more expensive than white beaded foam.
This information courtesy of http://www.flyingfoam.com
Joined Oct 2011
Foam density calculations
I have tracked down a supplier who can give me EPP with the following rating:
965mm x 580mm x 150 mm @ 3.3kg for the block.
However, I am not sure my calcs are correct and this seems a bit on the heavy side. Can someone please help me convert it to number I can compare in your # rating?
Australia, QLD, Acacia Ridge
Joined Dec 2011
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