I report the detection of interstellar Cai and CH at the velocity of the previously reported variable absorption component towards kappa Velorum (HD 81188). The very high spectral resolution (R approximate to 900 000) has resolved the intrinsic line profiles, yielding a kinetic temperature of T (k) = 190 (+170) (-150) K, and a line-of-sight tubulent velocity of v (t) = 0.26(+0.08) (-0.13) km s(-1), for the densest material. The Cai/Caii ratio implies a spatial density of n (H) greater than or similar to 10(3) cm(-3), although this may considerably underestimate the density in the variable region itself. The CH column density suggests a path-length of similar to10(2)to 10(3) au, supporting suggestions that variable interstellar components such as this are formed in extended structures (sheets or filaments) aligned with the line of sight.