https://www.reddit.com/r/AskHistorians/comments/26wopt/just_how_common_were_flaming_arrows_in_medieval/ by /u/Ambarenya

My understanding is that there was no substance that burned fast enough to get the 'fire arrow' effect we see in movies. Even on those occasions where fire arrows would be used they'd leave trails of smoke but wouldn't have that visual impact of flaming arrows we see in the movies.