Flash paper is a skinny, pretty flammable sheet that ignites close to abruptly whilst uncovered to flame

https://beckettxujn546.capitaljays.com/posts/18.-flash-products-review-what-to-look-for-before-purchasing

Flash paper is a thin, especially flammable sheet that ignites close to abruptly while uncovered to flame, producing vivid bursts of faded. It’s admired for technology demos and controlled lighting tricks.