Cotton is reliable in hot weather and a solid cotton dress in black or dark colors works for a funeral without feeling overdressed or inappropriate. Cotton blends with a small amount of stretch or a heavier weight cotton keeps the dress from clinging or looking too casual. A simple cotton dress without a lot of print or pattern respects the occasion. The cut matters more than the fabric detail because cotton is a straightforward choice. Look for dresses with structure at the waist or through the bodice rather than shapeless styles. A well-made cotton dress in a classic cut is what you reach for when summer heat is real but the occasion demands formality.