Polyester varnish impregnated single glass over heavy polyamide-imide overcoated polyester insulated rectangular aluminum wire 

Material B50D250 identifies polyester varnish impregnated single glass over heavy polyamide-imide overcoated polyester insulated rectangular aluminum wire not less than 0.040" conductor thickness as follows:
Description
Special tolerance and insulation requirements

Material Requirements
Conductor - Shall be high conductivity aluminum, Type EC，meeting the latest specification requirements for GE B12B20. The temper, defined by suffix to B12B20, shall be selected by the manufacturer to meet the insulated wire property requirements.
Enamel insulation - shall be heavy build polyamide-imide overcoated polyester, Class 220, conforming to the latest specification requirements for NEMA 36-a.
The degree of cure shall be controlled by color to limits established by the manufacturer to meet property requirements of the finished glass-insulated product, measured by the relative darkness detection using Macbeth Model Mc1010s "Color Eye" or equivalent instrumentation.

Glass yarn - Shall canform to the latest specification requirements of A2L4，A2L5,or A2L6 as applicable. Yarn supplied to industry equivalent specifications may also be used.