Okay folks,
After years of experimenting, I realized that most folks were going at shaping poppers backwards, using a dremel tool as a lathe rather than as a hand held grinding/shaping tool. What I am about to explain I have demonstrated in numerous conclaves and have so far made about a thousand flies -- obviously some better than others, but almost all better than most I see recommended on pattern sites. This approach is good for small panfish flies up to large tarpon flies. You get a smooth finished product.
If you want any details I don't explain below, don't hesitate to message me.
If you go to http://www.flytyingforum.com/pattern6910.html you will find what is likely the ultimate solution to popper making. I tried to provide as much detail in the instructions with that pattern as possible.
Note that super glue changes the chemical composition of the surface of closed cell foam and joining two pieces of foam with super glue creates one piece -- in other words, it's permanent.
Note also that if you go to Harbor Freight or www.harborfreight.com and buy a "9 Piece Hollow Punch Set" you can carve out cylinders of foam in 9 sizes for $5. You can shape the cylinder after punching with the dremel.
DO NOT try to make poppers out of flip flops. The interior foam is not dense enough to make a satisfactory fly. See foam buying instructions in the referenced pattern.