The sixteen-bar blues doubles the twelve-bar's first line: eight bars on the home chord before anything moves, then the familiar closing eight, with two bars of the subdominant, two of home, the dominant, the subdominant and home. It is the shape of Hoochie Coochie Man, where the long first half is carried in stop time, the band hitting together and falling silent under the voice, before the second half runs through the chords in time.
Reading it bar by bar
Eight bars on the home chord means eight bars in a row in which the flat third rubs against the chord's major third, a longer unbroken stretch than in any other form on this site. It is the same rub the twelve-bar opens with, held twice as long, and it is why the subdominant arriving in bar nine sounds like a door opening: the flat third becomes the chord's flat seventh and stops rubbing for the first time. From there the reading is the twelve-bar's closing eight bars, note for note, which is easy to check by setting the two tables side by side in the same key.
Holding one chord
A long stretch on one chord puts the weight on everything but the harmony: the feel, the riff, the voice. Read the flat-fifth column; it rubs in every bar here, as it does in every form, and across eight home bars it is the blue note a line keeps leaning on, bent up towards the fifth or let fall to the fourth. The fifth of the key, meanwhile, never rubs anywhere in the form. It is the one note of the scale that is safe in every bar, a chord tone over the home chord and the dominant and a colour note over the subdominant, which makes it a natural place for a phrase to come to rest after all that rubbing.