Sculptors tend to hew stone, hammer metal, or mold clay. Mr. Hackenwerth blows, twists, and shapes inflated plastic into configurations as magical and ephemeral as sand castles at the seashore. Mr. Hackenwerth draws inspiration from the plant and animal kingdoms’ “combination of spirituality and sexuality.” Of these plastic shapes, he said: “I’m filling them. The air inside is slipping out. It’s a great metaphor for our own lives.” The works sag with gravity over time, shrinking as they age, “a perfect combination of sadness and joy.” Mr. Hackenwerth’s work celebrates exuberance while transcending the carnivalesque.