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How to sew an insulated lunch bag

Posted by Maaike van Besien on

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
How to sew an insulated lunch bag using laminated cotton - maaidesign blog
Today I am sharing a simple tutorial on how to sew an insulated lunch bag. 
I designed this bag as I wanted something that would be easily adjustable to the contents.
I often find that the kids lunch bags are either too big or too small depending on what I decide to pack for them that day.
So this bag is adjustable in size, in a very simple way: just roll over the top until everything is nice and snug, then wrap the elastic band around it to keep everything in place. The elastic is stitched to the base of the bag so it doesn't get lost.
The inside if the bag is lined with laminated cotton, which is ideal when dealing with moisture from ice blocks or cold food. I used a fabric from my stash for the outside. I think jeans would work really well here too. 
So here is how you can make your own:
Supplies needed:
- Laminated cotton as bag lining (75cm x 30cm)
- External fabric (75cm x 30cm)
- Fleece fusable interfacing (75cm x 30cm) (or alternatively, use the inside of an insulated shopping bag)
- Bias binding, about 60cm
- Elastic, e.g. 20mm wide, about 75cm long.
- Thread
These instructions are for a bag with roughly the following finished internal dimensions:
- height: 30cm
- base: 13x13cm
I used a seam allowance of 1cm.
1. Cut a rectangle in laminated cotton measuring: 75cm x 30cm
How to sew an insulated lunch bag using laminated cotton - maaidesign blog



2. Fold in half and draw 2 rectangles on the folded corners measuring: 7cm by 6 cm (the 6cm being perpendicular to the fold, 7cm parallel to the fold). Cut the rectangles out.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
3. Repeat for the external fabric, and the fleece interfacing.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
4. Iron the fleece interfacing to the external fabric (so not the laminate!) , as per the interfacing instructions.
Note: If you do not have fleece interfacing, alternatively you could cut up an insulated bag from the supermarket and use the plastic foam material that is inside. Cut it to size and place it in between the internal and external bag before adding the bias binding (step 10).
5. Fold the laminated cotton piece right sides together and stitch the side seams with a seam allowance of 1cm. I used a stitch length of 3mm, shorter stitch lengths will leave the holes too close together resulting in a weak seam.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
6. With the wrong side still facing out, open up the to holes in the base and fold flat so that the sides meet. Hold in place with wonder clips, or whatever you have available, here I used paperclips. I tend to avoid using pins with laminated cottons as it will leave holes.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog

How to sew an insulated lunch bag using laminated cotton - maaidesign blog

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
7. Sew both sides at 1cm seam allowance. Your piece should now look like a bag with a flat bottom. Trim the corners.
How to sew an insulated lunch bag using laminated cotton - maaidesign blog
8. Stitch the middle of the elastic piece to the base part of the external fabric. I stitched a rectangle close to the edge of the elastic.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
9. Stitch the base of the external bag the as you did for the bag lining.
How to sew an insulated lunch bag using laminated cotton - maaidesign blog
10. Place the bag lining (laminated cotton) inside the external bag and line up, wrong sides facing. Again I used clips to keep everything in place due to the thickness of the combination of the layers. 

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
11. Stitch bias binding to finish off the top of the bag, and attach the two bags together. I used the 2 step method, where I opened up the bias tape first, and stitched it right sides together onto the laminate, and stitched in the folds first.  Then I folded it over to the other side and stitched it closed. If you use a tape that is 25mm wide, then your sewing foot will not touch the laminate so it is easier to sew. I also recommend using double folded bias binding which is easier than the one I used in the photo.
If you want to see this process in more detail, have a look at this blogpost where I add bias binding to a laminated tablecloth.
How to sew an insulated lunch bag using laminated cotton - maaidesign blog
12. To finish the bag, the 2 elastic ends need to be stitched together. Find the right length by filling the bag and rolling the top down to what seems a snug fit. Then determine the length of the elastic making sure it is stretched with the bag will be closed. 
13. I made a cover for the part where the elastic overlaps. This can serve as a nice spot to place a woven tag, or why not hand stitch someone's name here?
To determine the size of this cover, measure the length that you want to cover, add an extra 1cm to be on the safe side, and add 2x seam allowance, this is the length of the piece. For the width, take the width of the elastic, double it, add an extra 1cm plus add 2x seam allowance. 
Fold the ends in and press. Place over the elastic and stitch.

How to sew an insulated lunch bag using laminated cotton - maaidesign blog

How to sew an insulated lunch bag using laminated cotton - maaidesign blog
And there you have it, a simple insulated lunch bag, that will fit boxes in all sorts of shapes and sizes!
How to sew an insulated lunch bag using laminated cotton - maaidesign blog

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