This 9 5/8" x 11 5/8" First Class envelope is constructed of 28# paper. The envelope has offset cellophane windows that allows the taxpayer name and address to clearly show through. 

Top window is 1 1/2" x 4", 1 1/4" from the left side of envelope, 9" from the bottom of the envelope.

Bottom window is 1 13/16" x 5 5/8", 2 3/8" from the left side of envelope, 5 1/8" from the bottom of envelope.