Makeshift Flame Suppressor?

Hey! I was wondering if there is any such material that could serve as a flame suppressor. I am a avid Mil-Sim player (Military Simulations) and I am looking to make smoke grenades. I've already discovered the popular KNO3 + Sugar + Baking Soda mixture, but the problem with that is there is flame when the mixture is ignited and starts putting off smoke. So, when I'm constructing the smoke grenade body, I would like some sort of material that would contain the flame, but still let the smoke out. You're awesome for reading and thanks in advance!