Ribbon-type heating elements running lengthwise are encased in durable glass braid, then impregnated and covered with tough silicone rubber. Rubber insulates stranded terminal leads at one end and waterproofs fittings at both ends. Also permits high-moisture use and helps tapes resist most laboratory environmental conditions. Has attached cord with 2-blade plug. Temperature limit 480°F. Short, narrow tapes must be operated at reduced voltage, easily attained with a variable transformer.