Clearjel is a modified cornstarch used by professional bakers to thicken fruit pie fillings and in canning. There are two types of jel: Instant Clearjel and regular cook type clear jel. The instant has some advantages over ordinary cornstarch, because it thickens without cooking, works well with acidic ingredients and is able to tolerate high temperatures. Cook type clear jel works well with acidic ingredients and tolerates high temperatures and can be used in canning homemade pie fillings, since it doesn’t begin thickening until the liquid begins to cool.