Vowel hyper-articulation, usually identified from the size of the triangle formed from the corner vowels /i/, /a/, and /u/, often features in clearly articulated speech styles. It has been attested in infant-directed speech (IDS) and child-directed speech (CDS), reading-out-loud styles, and foreigner-directed speech (FDS), in numerous communities. It is as yet unclear whether reading out loud and FDS universally feature hyper articulation of vowels, but vowel hyper-articulation in IDS and CDS is decidedly not universal. Studies of Cantonese, Dutch, German, Japanese, and Norwegian IDS have shown that the IDS vowel space in these languages is either similar in area to that of adult-directed speech (ADS), or that the IDS vowel space has reduced area relative to the ADS vowel space, hence showing hypo-articulation. We examined vowel acoustics in CDS and conversational ADS in the Papuan language Nungon, spoken by 1,000 people in a remote region in NE Papua New Guinea. Previous work established that Nungon CDS entails optional use of consonant alteration, special nursery vocabulary, and special morphosyntax, but acoustics and prosody were untested. This study shows that Nungon CDS to children aged 2;2–3;10 lacks any indication of vowel hyper-articulation. But Nungon CDS still displays other common prosodic traits of CDS styles around the world: increased mean pitch, and increased pitch range. Vowels in Nungon CDS to two-year-olds differed acoustically from those in CDS to three-year-olds only in duration, with vowels in CDS to the younger group lasting significantly longer than those in CDS to the older group, which had similar duration to ADS vowels. Finally, we compared the acoustics of vowels in Nungon CDS and conversational ADS to vowels in monologue narratives that were produced with a non-native Nungon speaker as primary listener, hence can be considered FDS. The vowel triangles of the Nungon FDS monologues were significantly larger than those of either CDS or conversational ADS, indicating vowel hyper-articulation. Mean pitch and pitch range in FDS monologues, compared with CDS and conversational ADS, differed among women and men, possibly relating to cultural expectations of female and male storytelling and conversational styles.