Pair of official First Day Covers commemorating the Sixth International Philatelic Exhibition (SIPEX) held in Washington, D.C., May 1966 — a major U.S. stamp exhibition promoting the theme “Discover America.”

Includes both covers:

• 5¢ SIPEX Stamp Cover – Designed by Thos. F. Naegele, with a four-color engraved and lithographed cachet featuring Christopher Columbus and the U.S. “Discover America” slogan.

• SIPEX Souvenir Sheet Cover – Larger format sheet by Brook Temple, depicting the U.S. Capitol and Washington Monument framed by cherry trees; issued only at the exhibition and not through post offices.

Both are postmarked Washington, D.C., with clean impressions dated May 21 and May 23, 1966. Unaddressed, well-preserved examples of 1960s U.S. philatelic show memorabilia.

SIPEX 1966 • Washington DC First Day Cover • Discover America • U.S. 5¢ Stamp • Souvenir Sheet • Brook Temple design • Thos. F. Naegele • Philatelic Exhibition • Topical Columbus • midcentury U.S. postal history