The evolution of Bert.

Image As seen in / Year Notes
Sesame Street
Season 1
The original Bert had an immobile unibrow and his hair appeared to be unkempt in some sketches.
Sesame Street
Season 1 - Season 2
Bert's head shape is more refined, with a more flexible neck. He can scrunch his mouth. His eyebrows do not cover his eyes.

Sesame Street
Season 3
Bert gets an eyebrow mechanism, allowing his brow to move up and down. His eyes become slightly smaller, and his colors are more vibrant. By Season 4, his eyebrow becomes considerably thinner.
Bert season 6
Sesame Street
Season 6
Bert's skin is more golden. His eye focus is not as strong seemingly due to slightly smaller pupils. His eyebrow is much straighter.
Bert season 8
Sesame Street
Season 8
Bert has paler Antron fleece skin. He also has a much taller and rounder head. His eyebrow becomes immobile, and his eyes are smaller.
Sesame Street
Season 9
Bert's skin is darker. He has also regained his eyebrow mechanism, and the down motion is improved. His head and hair are slightly thinner, and he has sturdier shoulder joints.
Sesame Street
Season 14
Both skin and clothing colors are brighter. Also, Bert's nose is smaller and his head is more rounded.
Sesame Street
Season 21
Bert's head is slightly wider with even smaller, more separated eyes.
Sesame Street
Season 28
Bert has a taller head, his hair is most often combed upward (rather than messy like Ernie's hair), and he has a more rounded eyebrow.
Sesame Street
Season 30
Bert's head is shorter and rather thicker than the previous version. His eyes are positioned closer together and his nose is longer.
Sesame Street
Season 33
Once again, Bert's head is taller, much like the 1996-1998 puppet. His antron fleece skin appears smoother and lighter yellow, and his nose is more red-orange in color.
TomTom promo
Bert's head becomes thinner and his eyes are farther apart.
Bert 2013
Sesame Street
Season 44
This version of Bert is interchanged with the previous version. Bert's head is wider and slightly shorter. His nose is higher up, and his eyebrow is thicker.
Predecessor Puppets and Planning

Bert-and-Ernie sketch
Design sketches for Sesame Street
(circa 1969)
Early sketches immediately established the contrast between Ernie's horizontal stripes and general look and Bert's vertical stripes and leaner appearance.

Chroma key shirts

In order to accommodate Chroma key (i.e. blue or green screens), the stripes on Bert's shirt occasionally change color as to not be keyed out.