Molenaar painted in watercolors and oils. He is known for his impressionism-style art with mountain and desert landscapes the dominant theme in his works. He painted the highest watercolor in history, spending 10 days in a tent painting K2 from memory at 25,000 feet during a severe storm that hit during the 1953 expedition. With precious fuel for melting snow running low, his teammates made him drink the remaining water colored with pigments.