Item Number 80015 Use this First Class Mail alternate window envelope to mail any tax return or report. A blue interior tint adds security while the cellophane window allows the taxpayer name and address to clearly show through. This 9 1/2 x 12 envelope is constructed of 28lb paper Flap Opening on short side. White wove 28lb paper stock. Window Measurements: âTop Window Size: 1 3/4 x 5 1/2 âTop Window is 1 3/4 x 5 1/2, 1 1/8 from left, 8 7/8 from bottom âBottom Window Size: 2 x 6 âBottom Window is 2 x 6, 2 from left, 4 3/4 from bottom Pricing is for 100 envelopes