Safe, efficient, form-fitting heaters for evenly distributed applications of heat to round bottom flasks and similar shaped vessels. The heating elements are thoroughly enclosed in an insulating glass fabric that makes the mantle suitable for heating flammable liquids for which other forms of heating would not be safe. The glass fabric is covered with grounded stainless steel mesh providing extra safety in case of an accidental spill. Temperature limit is 450 ºC. Input must be regulated by a variable temperature controller (such as Catalog No. AP4434) to control heating and protect the heating mantle.