and , are typically protruded, whereas front rounded vowels such as German and are typically compressed. Back or central compressed vowels and front protruded vowels are uncommon, and a contrast between the two types has been found to be phonemic in only one instance.

There are no dedicated IPA diacritics to represent the distinction, but the superscript IPA letter or can be used for compression and for protrusion. Compressed vowels may be pronounced either with the corners of the mouth drawn in, by some definitions rounded, or