free-form 
adjective
Not conforming to a regular or formal structure or shape: a free-form jazz improvisation...
- The chosen shape was a genuine free-form structure impossible to analyze logically.
- A flowerbed in the shape of a circle, square, or octagon looks formal, while one with a free-form shape has a casual look.
- These tiles are characterized by slender lines, geometric shapes, or more free-form patterns.