The finished product is a custom laptop bag for an OLPC XO laptop computer, but these instructions could probably be modified for many portable electronic devices. The bag core is made of high density foam, reinforced with paperboard. The bag is trimmed in polyester belting, has an adjustable strap, and a parachute buckle closure.

Step 1: Gather Your Materials

1 yard of fabric ($6.99)
2 pieces of 14"x22" posterboard ($0.78)
1 plastic parachute buckle for 1" belting ($2.29)
1 plastic strap adjuster for 1" belting ($1.29)
3 yards of belting ($2.97)
27" of 1" high density foam ($8.24)
Thread
Sewing machine
Needles for hand stitching
Straight pins
Wax paper
Marker
Paper glue

The fabric I selected was from the calico/quiltmaking department, but I imagine you could use anything reasonably stable (not lightweight or flowy). Belt color should coordinate with fabric. I used two colors of thread, one to loosely coordinate with the fabric and one to blend in with the belt color. Consider your level of sewing skill if you want to use a contrasting color.

Step 2: Create the Pattern

Tear a piece of wax paper, about three times the height of the finished bag. For the XO bag, mine was 27" long. Place your computer on the paper. roughly trace a rectangle around your laptop at the center bottom of the wax paper. The top of the rectangle can be drawn as a dotted line. This will be the front of the case pocket (not the flap).

Directly above that rectangle, draw a 2nd rectangle that is the thickness of your laptop, plus a little extra space. This will be the bottom of the bag. The top of that rectangle can be drawn as a dotted line.

Directly above that rectangle, draw another rectangle the same size of the first one. All sides of this rectangle can be drawn as dotted lines. This will be the back of the laptop case. To the sides of this rectangle, draw two rectangles that will be the sides of the bag. The width of these rectangles should be the thickness of your laptop.

Finally, at the top what you've drawn, draw another rectangle that will be the flap. My flap is roughly 4/6 the size of the bag.

Cut the pattern out on the solid lines and try out the fit by wrapping the pattern around the laptop as if it were the finished product. Make any necessary adjustments. Keep in mind that there will be a layer of foam between the laptop and the material that is represented by the pattern.

Step 3: Cut the Paperboard

Cut the paperboard to match the pattern. The cut paperboard rectangles will be the size of the "Back of bag", "Bottom", and "Front of bag" sections of the pattern (see the blue shaded area of the illustration). Cut one of these shapes out of each piece of paperboard, then glue the two paperboard rectangles together with regular paper glue. Draw two lines to separate the three sections of the pattern.

Step 4: Fold the Paperboard

Use a straight edge to fold the paperboard on the lines that you drew. I went over the folds with the handle of my scissors to make sure the fold was crisp.

Step 5: Cut the Foam

Trace the pattern onto the foam, and cut it out. Wrap the foam around the laptop to check the fit.

Step 6: Cut the Fabric

Please note that the pattern you created is not actually the pattern for the fabric. It is just the finished size of the sewn bag. You will need to account for seams!

At this point in the process, I really started to wing it. I started with the fabric which was already folded lengthwise, with the "wrong side" of the fabric on the inside. I placed this folded fabric on top of the paperboard and foam. This way, I was able to cut out two pieces of fabric at once. I cut out the basic shape of the pattern, with about a 2" seam allowance on all sides. I was obviously making this up as I went along.

Step 7: Put the Layers Together. Sew All the Way Around.

In this step, you will create a kind of sandwich:
- Fabric (the outer fabric of the bag)
- Foam
- Paperboard
- Fabric (the inside of the bag)

At this point, it would be nice to use some spray adhesive to glue the outer fabric to the foam. I didn't use any. I put the pieces together in the appropriate order (fabric, foam, paperboard, fabric and I sewed all the way around the foam, using a machine. I didn't sew the foam, just as close to the foam as I could. Be extra careful to make sure that the fabric remains taught on both sides of the sandwich as you sew around the perimeter. If you're using adhesive, this will be less of an issue.

The extra fabric around the edges will allow you to put the bag together later.

Hem all edges, by rolling the fabric over twice 1/4". Visible edges are the sides that flap out, and the front edge of the bag (not the flap edge, but the front edge that was the bottom of the pattern). Take special care to make these hems look nice.

Step 8: Check the Fit

Wrap the bag around the laptop to check the fit. (In this picture, the edges have not been hemmed yet, but you get the idea.)

Step 9: Attach Trim

Measure belting to fit all the way around the front flap. Add a total of 1" for hems. Hem each side by rolling 1/4" under twice, and sewing along the edge. (I didn't do this, but I wish I had!)

Pin the belting around the flap, and sew using the machine and thread that matches. Pay special care to the way the belting goes around the corners. You will need to fold the belting over on itself a little to make it look nice. I tried to sew toward the edge of the belting.

Step 10: Sew the Sides

Pin the side flaps onto the front of the bag, while the laptop is inside the bag. Fold the bottom of the side flaps in, as if you were wrapping a present.

Make sure the fit isn't too tight. Try pulling the laptop out of the bag with it pinned, and try putting it bag in again to check the fit. The rubber "feet" of the XO grab the fabric a bit, so I didn't want my fit to be too tight. If you need to, readjust and repin.

Hand stitch the sides of the bag. This is painful and tedious. In my case, I ended up having to sew through foam and paperboard, so it would help to use a thimble or two to help you push the needle through the paperboard.

Step 11: Add the Strap

Figure out how long the strap should be for the laptop owner. Add several inches to this amount for hems and for the strap adjuster (I added an extra 5"). Cut the strap into two pieces (one about 10" long) and hem all four edges by rolling them over twice 1/4". Put two edges of the strap into the adjuster, following the instructions on the package. This will involve sewing one side of the strap onto itselt, stitching an "x" inside a square. Use the same stitch pattern onto the sides of the bag. I did this by hand.

Finally, cut two additional pieces of strap. Hem the edges of these as you did the others. Attach these to the parachute buckle, following the instructions on the package. Attach one strap and buckle half to the front flap of the bag, and the other strap/buckle to the front of the bag.

C'est tout!