Pannier totes comes in two basic types, hard sided and soft sided. These different types of styles allow for several basic strategies: you can use a hard sided bag to provide the contents with some extra support and protection at the cost of being able to stuff some extra things into a bulging soft sided bag.
Hard sided models are basically soft-sided panniers with a molded liner which acts as a framework. The hard liners are often super tough, roto-molded construction. Sides are curved to fit your bag and allows for a lower slide clearance. It makes for a neat, clean interior.
Typically, a soft-sided pannier is shaped like a bucket with a round or oval bottom base and is usually longer in its height and shorter in its width. Often they feature a drawstring closure.
Sometimes a pannier has one single strap handle just like a basket but other times it has two as in a tote bag combination style. It can be designed to carry in your hand, on your shoulder or across your chest. Strap attachment points can be riveted within the body for extra strength.
Selecting a Liner
Whenever selecting a liner of a pannier, look for a container that will be roomy enough to carry your belongings. Look for something deep. It will provide the “basket-shape” of your bag so keep this in mind as well. Search out containers that have no sharp edges or seams. This will allow for a smoother fit within the cloth portion of the bag. Keep the mouth (top) larger than the bottom, or at least equal to its sides so that you can insert the liner into the cloth body of the tote. Choose a container that has rounded corners (no sharp angles), or has a round or oval bottom. This will allow for as few seams as possible. Here are a few ideas for liners: plastic food storage containers, metal tins, smooth straw baskets, cardboard boxes, vegetable baskets, nesting pots.
Making the Pattern
Begin by tracing out the bottom of the container onto grid paper. This will be the base pattern piece.
Now, plot out a rectangle shape onto grid paper equal to the height (H) and the width (W) of the top edge (open lip) of the container. From the center of the rectangle, plot out half of the bottom width (½W) measurement on either side of center on the lower part of the rectangle. Join the top corner to the plotted lower location with a straight line on both sides of the rectangle. This will be the side piece.
Next, repeat the step above for the depth. Draw a rectangle shape equal to the height (H) and depth (D) of the top edge (open lip) of the container. From the center of the rectangle, plot out half of the bottom depth (½D) measurement on either side of center of this rectangle. Join the top corner to the plotted lower location with a straight line on both sides of the rectangle. This will be the gusset piece.
Drafting a Seamless Pattern
Now, that you have a 2-D drawing of the sides of your container, you want to make up the pannier’s body pattern piece by joining them together.
Cut the gusset pattern through its center along the height (vertical cut). Align and match the 2 gusset pattern pieces to the height of the side pattern piece and trace out the half-gusset portions. At the chevron points, blend smoothly with a curved line. This is the body pattern piece.
Create a closure for the bag. Typically, it is a drawstring closure that would cinch up the opening of the bag and allow easy access to the interior. However you may choose to insert a zipper or a toggled flap for additional security.
For the drawstring closure, draw a rectangle, with its length equal to the width + depth (W+D) of the container; and its width equal to the depth (D) of the container (open lip edge).
For a zipper closure, extend the side seams of the body pattern with tangent lines equal to half of the top depth (½D) measurement. Join these two points with a straight line drawn across the top. Measure the distance across the container diagonally from opposite corners and round up to the next inch. This is the length of zipper required. Plot the zipper opening equal on either side of center across the top of the body pattern piece.
Here is a tutorial on how to create a DIY pannier handbag.