The unique appearance of the Plushcap has made this species a taxonomic riddle for decades. The golden-yellow forecrown consists of stiff, plush-like feathers. Its underparts and sides of the head are rufous, while the upperparts are dark bluish gray. Its stubby, rounded bill is also unusual. Male and female are similar in plumage.
The Plushcap's distinctive plumage makes it unlikely to be mistaken for another species. The Golden-crowned Tanager (Iridosornis rufivertex) may be confused with the Plushcap, due to its overall similarity in its pattern; both have a yellow crown patch (Ridgely and Tudor 1989). However, the Golden-crowned Tanager is mainly blue, whereas the Plushcap has rufous or chestnut underparts and bluish gray upper parts (Ridgely and Tudor 1989, Ridgely and Greenfield 2009). The Black-eared Hemispingus (Hemispingus melanotis) often is found in the same flocks and also resembles the Plushcap. The Black-eared Hemispingus, however, lacks lacks the yellow crown patch (Ridgely and Tudor 1989).
Adults: Sexes alike with a short, thick stubby, swollen black bill (Hilty and Brown 1986, Hilty 2003). The forecrown consists of plushy, velvety, extremely dense and stiff golden yellow colored feathers (Meyer de Schauensee 1964, Hilty 2003). These dense plushy feathers are believed to resist wear, and to be effective in resisting moisture from bamboo whorls that are usually wet from rain or fog (Hilty et al. 1979). The lores, hindcrown, eyering and nape are black, and the rest of the upperparts are blue gray. The tail is strongly graduated and fan shaped (Meyer de Schauensee 1964, Hilty and Brown 1986, Fjeldså and Krabbe 1990). The sides of the head, cheeks, sides of neck and underparts are a rich chestnut brown (Ridgely and Tudor 1989, Hilty 2003).
Immatures: Duller. Except where indicated otherwise, the following description is based on Hilty et al. (1979). The upperparts are uniformly brownish olive. The wings are dusky, the feathers narrowly edged with brownish olive. The upper surface of the rectrices is dusky, the feathers broadly edged with brownish olive; the underside of the rectrices is brownish olive, paler than in adults. The underparts are light brownish olive, heavily washed with ochraceous-tawny. The immature crown feathers are somewhat plush-like, but gray with a yellow base (Fjeldså and Krabbe 1990). Some immatures approaching their adult plumage display various amounts of yellow on the basal portion of the feathers on the forecrown, as well as specks of rufous or chestnut underparts.
Juvenile: The plumage is similar to that of the immature, but is grayer above and has less contrast between the forecrown and hindcrown (Fjeldså and Krabbe 1990). The feathers on the forecrown have no yellow at the base of them; the underparts are dark gray brown (Fjeldså and Krabbe 1990).
Iris: Brown, dark brown, pale brown (Field Museum of Natural History)
Bill: Black (Hilty 2003, Field Museum of Natural History)
Tarsi: Black, dark brown, dark gray (Restall et. al 2007, Field Museum of Natural History)
Total length: 14 cm (Ridgely and Tudor 2009)
Mass, males (adult): mean 14.9 g (n=16); males (juvenile): mean 13.5 (n=2) (Remsen 1985)
Mass, females (adult): mean 13.4 g (n=8); female (juvenile): 12.5 (n=1) (Remsen 1985)