Sure, they're flammable. But the amount of BTUs in, say, packaging, is negligible, because it's so lightweight. When you combine lots of recycled packaging in

Sure, they're flammable. But the amount of BTUs in, say, packaging, is negligible, because it's so lightweight. When you combine lots of recycled packaging into dense bricks, it becomes a lot of dense BTUs, so can provide a lot of fuel to a fire.