Vowels: Height, Backness, and Rounding. The combination of height, backness, and rounding creates a multi-dimensional vowel space. For example, high, front, unrounded /i/ contrasts sharply with high, back, rounded /u/, demonstrating how these three articulatory features differentiate vowels perceptually and phonetically. Rounding describes the shape of the lips during vowel production. Rounded vowels, like /u/ and /o/, involve lip protrusion, while unrounded vowels, such as /i/ and /æ/ (as in "cat"), are produced with relaxed lips