I get asked quite often the differences between EPP and Depron so here is a little article that will hopefully help the list the differences.
Size / Thickness
The most commonly used thickness for scratch building RC airplanes is 6mm depron. The length and width is only determined by your project
A well built Depron airplane flies very precise, like its is on rails.
Depron is very rigid and only requires carbon reinforcements on the high stress points such as a wing spar and elevator spar and in some extreme circumstances and fuselage spar.
Depron foam most times snaps or cracks when it reaches it maximum stress point. Stress failures are easily combated by adding a carbon fiber tube on high stress areas on the RC airplane. Be sure to use epoxy, very sparingly, to glue in spars.
Depron requires the need of special foam specific glues such as the foam safe glue and foam safe accelerator carried at graysonhobby.com
You can use epoxy and hot glue to build with depron, but this adds a tremendous amounts of weight to your build. Weight is not your friend when building airplanes of any size. Epoxy is a great for structural crash repairs, but I try to limit the amount of Epoxy.
CAUTION. The use of regular CA will burn and ruin your depron, so its very important you use the foam safe glue with accelerator. The accelerator is not mandatory by the manufacture, but I sure feel it its.
Another great glue for depron is the Foam Tac glue which according to the manufacture is specifically designed for depron.
GraysonHobby sells foam safe paint. This paint will not eat your depron foam and this is the paint that I use on all of my airplanes. Paints you purchase at anly local hardware or big box store most often will eat the depron. So be sure to test your paint on scraps. (if you do not have any scraps, then you are not flying hard enough ☺
With typical flying and moderately use, aka no crashing, you can figure for every 10 flights on a depron plane, you will spend about 10 minutes for repairing. If you crash your airplane hard, forget the repair and start the rebuild.
Now for EPP
Size / Thickness
The comparable size of 6mm depron is 9mm EPP. Graysonhobby.com sells factory cut sizes at 24 inches x 36 inches.
EPP foam is much much more flexible than depron, so EPP airplanes do not fly as precise as depron. Now you can tape your EPP from front to back and it really strengthen up the EPP, but adds a TON of weight
EPP airplanes require carbon spars. How much depons on the type of airplanes, but it will require carbon.
EPP tears when it reaches its stress point, but is easily repaired.
For EPP I personally use Foam Tac and hot glue to build and repair. Yes I know this goes against what I said about depron, but lets face it, depron is for crash and bashing so I build EPP planes for crashing.
EPP is considered crash resistant but that all depends on your airplane and you definition of broke. I personally have flown a parkjet into the ground with a super mega jet going over 100mph with zero damage. The plane bounced nearly 10 feet high and the battery was effect, but the plane and literally no damage.
EPP it’s heavier than Depron but EPP is better for beginners.
A good tip for building EPP 3D type airplanes is to use a KF airfoil strip on the wing. It will make the plane fly better and makes the wing much stronger with not as much bracing, the theory being ,with less solid material to break
High speed EPP planes will need a considerable amount of bracing when using the KF air foil unlike depron airplanes.
So now that you are really confused, here is a quick summary.
Epp is more flexible than depron and usually needs some carbon reinforcing, especially in the wing although so does Depron. 1 square inch of 9mm, 1.3 lb/ cubic ft Epp weighs in at .12 grams. 1 square inch of 6mm Depron weighs in at .14 grams. I’ve built and flown planes made out of both and the EPP will take far more punishment if you are a beginning flyer/builder. Depron is slicker looking but breaks up much more quickly in an accident.