Its phonation is voiced, which means the vocal cords vibrate during the articulation. However, in some languages (like Swiss German) it can just mean that this consonant is pronounced shorter and weaker than its voiceless counterpart, while its voicedness or lack thereof is not relevant. In such cases it's more accurate to call such sounds lenis or lax.
It is an oral consonant, which means air is allowed to escape through the mouth only.
It is a central consonant, which means it is produced by directing the airstream along the center of the tongue, rather than to the sides.
Allophone of [ɾ ~ ʁ] in recent loanwords, used even by many speakers who do not use coda alveolar, post-alveolar or retroflex approximants in native words. Varies individually. Generally not as onset or final e.g. trailer[ˈtɾejle̞ʁ].
Some or all coda /ɾ/ may instead be a guttural or an approximant, varying by speaker, albeit more likely to be aspirated or deleted altogether than to be an approximant among native speakers when as final. See Portuguese phonology.
Allophone of [ɾ ~ ʁ] in the syllable coda. May also be retroflex, post-alveolar and/or rhotic vowel. As most rhotic coda in colloquial Brazilian Portuguese, likely to get deleted as final or at the end of sentences.
Browman, L.; Goldstein (1995), "Gestural syllable position in American English", in Bell-Berti, F., Producing Speech: Contemporary issues for K Harris, New York: AIP, pp. 9–33
Cornyn, William (1944), Outline of Burmese Grammar, Supplement to Language, vol. 20 no. 4, Baltimore: Linguistic Society of America
Delattre, P.; Freeman, D.C. (1968), "A dialect study of American R's by x-ray motion picture", Linguistics44: 29–68
Engstrand, Olle (1999), "Swedish", Handbook of the International Phonetic Association, Cambridge University Press, pp. 140–142, ISBN9780521637510
Fougeron, C (1999), "Prosodically conditioned articulatory variation: A Review", UCLA Working Papers in Phonetics97, pp. 1–73
Grønnum, Nina (2003), Why are the Danes so hard to understand?
Hallé, Pierre A.; Best, Catherine T.; Levitt, Andrea (1999), "Phonetic vs. phonological influences on French listeners' perception of American English approximants", Journal of Phonetics27 (3): 281–306, doi:10.1006/jpho.1999.0097
Ikekeonwu, Clara I. (1999), "Igbo", Handbook of the International Phonetic Association, Cambridge University Press, pp. 108–110, ISBN9780521637510
Kohler, Klaus (1995), Einführung in die Phonetik des Deutschen, Berlin: Erich Schmidt Verlag