Depends on the process. White Energy and CoalTek microwave processes both rely on binderless briquetting and in both instances, the coal must be heated substantially prior to briquetting. For ambient temperature briquetting, a variety of binders have been used including asphalt, starch, lignin, and molasses/lime among others. There is no perfect binder, it all depends what on strength and resistance to water degradation required and what is available locally at the most reasonable price.