Most flip flops are either too stiff, or don't have enough support for my arches. I made a pair with simple leather straps and cut the soles from a 1 1/2-inch thick foam kneeling pad. These are what I would consider "light duty" sandals, so don't plan on doing any serious hiking in them. Also, your footing will not be as secure as with more rigid sandals. Due to their light weight, it can be easy to catch the toes on things (which is why I recommend trimming the toes a bit). It takes a bit to get used to walking in these, so be careful or carry band-aids.

Supplies

1 - Dense foam kneeling pad (1 1/2-inch thick).

4 Leather strips, each about 7-inches long (2-ounce, cut 1-inch wide, for straps)

2 - Leather strips, each about 5-inches long (same material, cut 3/8-inch wide, for the toe-loops)

Assorted small leather trimmings (3/8-inch, for backing the foam where the straps attach)

Jigsaw with foam cutting blade.

Leather Punches

Awl

Needles and strong thread (for saddle stitching)

Contact cement

Needle nose pliers

Step 1: Cut Out Soles

I just used a pair of flip flops that fit me as a pattern for these, tracing the outline, and using an awl to mark the mounting points. For this black foam, a white gel-pen makes a good clear line to follow.

I have this wavy "foam-cutting" blade for my jigsaw, and I sharpened it a little with a round file before cutting this dense foam. The weight of the saw will bend the foam, making an angled cut, instead of a good square edge, so keep the blade close to the edge of the surface that is supporting the foam.

Try to make long, slow, even cuts. It's actually easier to hold the saw in position, close to the edge of the support table, and slide the work piece under the saw. This requires holding the weight of the saw a bit, but it is easier to keep the saw vertical this way. Of course, if you happen to have a band saw, lucky you.

Step 2: Make the Straps

The straps seem complicated, but they're just strips of leather cut at 45-degree angles, sandwitched between the two ends of the toe-strap, glued together and sewn. The strap on the outside of the foot is about 5/8-inch longer than the one that anchors under your instep. I just wrapped the straps around my foot to guess where to cut them.

We'll check the fit and trim the straps as needed, after attaching the toe loops to the soles.

I cut the ends at 45-degrees (both ends in the same direction). [Note: it's probably better to have the straps at something less than a 90-degree angle, so like a 43- or 44-degree angle would be good here, but it isn't rocket surgery, and leather stretches.] Pair up the ends (one long, and one short) and make marks so you know where the toe-loop will be glued. The underside of this right-angle seam won't show, but on the top side be careful not to get glue on the parts that show. I just laid the 3/8-inch wide toe-loop material on top of the joint, and scratched faint lines with the awl to mark where to stop applying the glue. Let the glue dry till it's tacky, and press the toe-strap part in place.

Turn the piece over and apply glue the to the other side of the seam and to the part of the toe-loop that folds over the seam. When the glue is ready, fold the toe-loop over to cover the seam. Give the glued joints a few taps with a mallet to make them solid.

Note, you will be stitching these parts together, so make sure the toe-loop part overlaps the seam by enough for a row of stitches on each side of the seam. It will be easier if you use a wider strip of leather for the toe strip, but if you make it too wide and you'll get blisters.

Punch holes for saddle stitching the right-angle seams. Make sure that the stitching holes catch the side straps and the toe-loop leather on both the top and the bottom. You want this right-angle seam to be good and strong. I just started stitching at the toe-loop and stitched up one side and back down the other, ending by pushing the needles through at an angle, so they come out on the inside of the toe-loop. Tie the threads off, with few overhand knots, hiding the knots inside the loop.

Lastly, I used a four-hole punch to make larger holes in the ends of the straps, and in the matching bottom pieces. You could do this just as well with an awl, nobody is going to see these stitches.

Step 3: Stitch the Straps to the Soles.

The four holes in each end of the straps will match up with holes in the strips that go on the bottom.

Use an awl to poke a pair of holes where you marked the anchor point for the toe-loop. Thread a needle and sew the toe-loop down with several passes of thread through the sole, using the two-hole bottom piece to keep the thread from cutting into the foam. Snug the toe-loop down good and tight, as this will loosen up as the soles compress.

To fit the straps to your feet, stand on the sole, with the toe loop between your toes, and curl the strap around your foot. Use thumb tacks to anchor the straps in position for a test fit. The straps should be a little snug. Once I had the straps anchored at the correct length, I marked the locations for where to anchor each strap. (I decided to cut off some of the excess material from each end and punched new holes in the ends of the straps).

Using the marks, push the awl through each of the four holes where the strap will be mounted, keeping the awl as straight as possible, so you can line up the holes on the top, with the holes on the bottom piece. Do your best to line up the holes, but it doesn't have to be perfect. It may be easier to punch the holes with the awl as you are stitching the straps to the soles. Stitch the strap and bottom part together very snugly, compressing the foam a bit if you can.

Note, you can always re-tie (or move) these connections if the straps get loose.

That's it, your soft summer flip flops are ready to wear. You can add some sort of finish to the leather, but I'm just leaving these plain.