The US Postal Service notes that exposure to ultraviolet (UV) light causes degradation of thermochromic inks, so the eclipse stamps should be shielded from sunlight to preserve their thermochromic behavior. To help with this, the Postal Service sends panes of this stamp to purchasers in special UV-blocking envelopes.[7] In addition, UV-protective sleeves for the eclipse stamps are available from post offices for 25¢ each.