Natural lump, I haven't found any difference between name brands and cheaper store brands. It doesn't take as much as the briquets to generate a lot of heat and it has no chemicals. Ive often wondered what all kind of chemicals may be in the briquets. Just make sure it is hardwood and not anything else. One trick since you are wanting to be frugal. GDG taught me this.. When you are through cooking pour a gallon or so of water on the coals and put them out. They will quickly dry and you can use what is left next time, this makes a bag go a lot further.