How to build a foam cored PVC recurved reflex longbow.

Want a cheap bow? For 15 bucks, you can get a 10 foot length of PVC pressure pipe and make your own. You don't need a hot air gun. The heat from a stove or even a blowtorch would do. Just don't let it burn. The foam core jacks the price up to around 23 dollars. This makes it stronger, but I don't know how it affects the bow's action. I'd need a chronometer and newton scale to figure that out, and unfortunately I lack these tools.