Here is an article I did last year, but it is still relevant today. Undercutting has been around since the 80’s in one form or another, the “Pob”, Posh’s New Look Bob, is a combination of an undercut and a Bob.This is how to create it.

First, part the hair into four sections, To do this, take a centre parting from the front of the head to the very back of the head, an part the hair into two equal sections.  Then take a parting from the crown of the head to the back of the ear, ideally just at the top of the ear, this will part the hair into front and back sections, do the same on the other side of the head. You should now have the hair split into “Quadrant sections”. 

From the occipital bone in the centre at the back of the head, take a diagonal section from the centre parting, to the bottom of the back of the ear, do this on both sides of the head, and clip the hair out of the way.  Comb down this inverted “V” section, this is the area we are going to Undercut. Cut this hair like you would a uniform layer cut, try to leave the outline soft and “feathery”.

Once you have achieved this, that is your undercut done, the point of this is it is to remove bulk from the haircut underneath, and to remain “Disconnected” from the rest of the haircut.  Comb the remaining section down and cut into a Graduated Bob shape, increasing the length through the side areas. Texture the back of the hair taking a little weight out of the ends so they are not too blunt, this gives the haircut a now-a-day feel, and is important to the over all finished look.

Finish the sides of the hair like a traditional Bob, but again taking some weight out of the ends to give a softer look, you can do this by using layers from the crown to the longer outline of the haircut in front of the ears, making sure you do not cut too much weight out of the outline, as you need the long length in front of the ears for the haircut to work. Shape the fringe section to suit your client and you should have a new look for your collection. 

We are now going to only work on the back sections. From the back of the head feel for the occipital bone, this is the lump you can feel if you stroke your hand from the crown of the head to the nape area, roughly in the middle of the head.