How to make an insulated lunch bag

1. Materials & tools

Materials (standard, one-tier)

• Main fabric (oxford, quilted cotton or canvas) — about 60 × 60 cm (24 × 24 in)
• Lining fabric (insulating sheet or water-repellent fabric) — the same amount
• Webbing or a self-fabric handle — the length you chose, × 2
• Optional: hook-and-loop to close the opening

Tools

• Sewing machine (or needle and thread)
• Fabric marker or pencil
• Ruler and scissors
• Iron
• Pins or clips

2. Make the pattern (auto-generated in Katagami)

With the Katagami pattern tool, you just enter the finished size and it drafts a seam-allowance-included pattern, tiled to print at actual size on Letter or A4.

1. Open the tool
   Open the pattern tool and choose “Bags” → “Insulated lunch bag” from the tabs at the top.
2. Enter the size
   Enter the lunch box width, depth and height, and the handle length and cut width. Presets cover one-tier, two-tier and large.
3. Set the seam allowance
   Use the slider at the bottom (beginners: 1.0–1.5 cm / about 3/8–5/8 in).
4. Print
   Press “Print (actual size)”, then in the print dialog set Scale = 100% and turn “Fit to page” OFF. Check the 50 mm calibration box on the first guide sheet with a ruler.

3. Cutting the fabric

1. Measure the lunch box
   Width, depth and height. If an ice pack goes in too, add its thickness.
2. Trace the pattern
   Trace the body (base on the fold) and the handles.
3. Cut
   Cut the body in main and lining, and two handles. Insulating sheet can be left raw.

4. Sewing

4-1. Make the handles

1. Fold self-fabric handles in quarters and topstitch, or cut webbing to length and seal the ends.

4-2. Sew the main body and gusset

1. Fold the main body at the base, right sides together, and sew both sides.
2. Pinch each base corner into a triangle, matching the side seam to the base fold exactly.
3. Sew across at the depth of the lunch box. Check both sides measure the same before you sew — this is what decides whether the box sits level.
4. Trim the triangles to 1 cm.

4-3. Sew the lining

1. Make the lining the same way, leaving a 12 cm (5 in) gap in one side seam.
2. Insulating sheet is bulky — press its seam allowances to one side rather than open.

4-4. Join and finish

1. Turn the main bag out and slip it inside the lining, right sides together.
2. Catch the handle ends front and back as you sew around the opening.
3. Turn through the gap, close it, push the lining in and topstitch around the opening.

✏️ Both gussets must be identical. If the side seam and base fold are not exactly aligned when you pinch the triangle, one side ends up deeper and the lunch box sits at an angle — which is how it leaks.

5. Tips & variations

• Insulating sheet as lining: sold as thermal or foil-backed sheeting. It makes a real difference in summer.
• Close the opening: hook-and-loop across the top improves insulation and stops things falling out.
• Two-tier boxes are tall: taller than people expect. Use the two-tier preset or measure.