Woven bars are great fun to make. Traditionally threads are with drawn from the foundation fabric and new threads are woven in but with freestyle bars you work them on the surface of the fabric which means they become a raised stitch. You can work one layer then another on top making them create depth and interest 

The sample is worked in perle 5 and I have used a contrasting coloured thread so that you can see what is happening. Most often threads are not contrasting. 

To start a woven bar  work an even number of straight stitches. I have used 6 here so you can see very well what is happening but I could have used 2 or 4 

Don’t work them too tightly as these are the foundation stitches that will be woven.

To weave use a tapestry needle as the blunt end will mean you do not split any of the foundation threads. 

Bring your thread out from the back of the fabric to the left of the first straight stitch.

Take the thread over three stitches and then under three stitches. Weave don’t sew as you are not taking the needle through the fabric but weaving the foundation stitches. 

Turn you needle and take the thread over  three stitches and then under three stitches 

Repeat this back and forth action.

Pack your stitches slightly by gently nudging them up the bar.

When you have worked the bar take your weaving thread to the back, tie off the thread and trim.

(Sorry the photograph got it self flipped to the side but I am sure you can see how it is meant to be.)