Next I did the same with the liner fabric and the Insul-Brite. When I seamed the sides and bottom, however, I took a slightly larger seam, say 1-2 mm deeper, to help the bulk of the liner and insulation fabric fit inside the outer layer. Make sure to lay the liner fabric on the inside of the Insul-Bright so that the liner fabric will be on the RS. Sew around the top, through the 2 fabrics, 3/8" from edge to keep it from sliding around.
The next step was to square off the bottom of each rectangle, separately. Working with the liner rectangle first, open it up and refold it with the seams in the middle of the sides, folding the bottom a bit like Kermit the Frog's head.
I checked my measuring by holding the two points together to see if the ends lined up. They did. (Yay!)
Then I turned the outer layer RS out and placed it inside the inner layer, lining up the bottom edges and alternating the side seam so as not to make too big a seam to have to sew through. I pinned the seamed sides and then half-way between them to keep the unlined layer from stretching out of shape as compared to the lined layer, and to make sure my 2 layers fit together evenly. I left the back open for turning and to insert my elastic button loop. I like to use these tiny hair elastics because they come in so many nice colors. Also I have them all over my studio since they are my favorite knitting stitch markers.
I pinched the seamed edge of the elastic together and tacked it into place when I sewed up the opening by hand.
Almost done now, I pressed the edge flat and edge stitched around the top 1/4" from the edge. This also reinforced the elastic loop.
Finally, to give my hubbie the ability to make his lunch bag fit the amount he packed for the day, I sewed, not 1, but 3 buttons, centered down the front (that is to say the opposite side from the side with the loop).
All done! Yay! I think he will like it. I can't wait to give it to him for his birthday next week.
To recap the materials I used:
2 fat quarters
1 fat quarter of Insul-Bright
thread
3 buttons
1 small elastic hair band.