Shape
Stamps are commonly rectangular, but can also be circular, triangular, pentagonal, or irregular.
Material
Stamps are typically made from paper, but can also be made from other materials like foil, wood, plastic, or synthetic chemicals.
Text
Stamps can include text such as the country's abbreviation, the value of the stamp, or other information.
Phosphor marking
Stamps may have a hidden phosphor marking that helps sorting machines separate first and second class mail.
Office stamps: Common office stamp sizes include:
Small: 0.5 x 1.5 inches
Medium: 1 x 2 inches
Large: 1.5 x 3 inches
Extra large: 2 x 4 inches