Materials other than normal paper.
USA
USA Experimental Plastic Stamps - 25c dollar sized vending sheet
Sold for six months only, from May 18, 1990 from 1st Nat'l Bank of Seattle automated teller machine. Scott No. 2475a
$
5.00
USA Experimental Plastic Stamps - F-denominated (29-cent) dollar sized vending sheet
Sold from Jan 22, 1991 from the 1st Nat'l Bank of Seattle automated teller machine. Scott No. 2522a
$
6.50