For hiking, I wanted a small lightweight raft for crossing
rivers and creeks, that I can easily toss into my backpack and carry with me. The design should be very basic, just two layers of fabric welded together to from the tube and floor, with a valve added, like the Klymit design or the Halkett boat (https://en.wikipedia.org/wiki/Halkett_boat).

Step 1: Introduction

Nowadays you don`t have to sacrifice your rain cloak, as
there is TPU coated fabric available that can easily be welded together using a heat sealing iron.

But before building the actual raft based on my design, I
wanted to make some prototypes (inflatables sometimes behave strange I had to find out).

Step 2: LDPE

I didn`t want to use the expensive TPU material, so I
started using LDPE film (100 my thickness) I had lying around. But heat sealing iron didn`t work as expected, gluing doesn`t work with LDPE, so what could I do?

Step 3: The Problem..

Having access to a CO2 laser cutter, I thought that it might
be possible to reduce the cutting power to near zero and increase the speed to weld two sheets of LDPE together- but it either had no effect on the material at all or the laser beam cut right through it.

Step 4: Solution

Then it dawned on me: if I set the laser beam to be out of focus, it
automatically widens the beam, thus affecting a larger area and also reducing the amount of energy applied per mm². In my first try, the two sheets of LDPE film were welded nicely together.

All I had to do was move the lens holder to the top position and play around with the power and speed settings. And make sure the material lied really flat, as wrinkles affect the quality of the seam.

It is also possible to weld and cut with the same file, no
need to stop and refocus for cutting- just use more power to cut through the material, the cutting edge won`t be perfect as the beam is out of focus, but in my case it didn`t matter.

Step 5:

I didn`t stop with making prototypes for my
raft, but made all kind of oddly shaped inflatables, as you can see. You can also fill them with water, make lamp shades,wearables or ice”cubes”... there is no limits.

I use an old 60 watt CO2 laser, so the settings provided in the file attached might not work with your machine, but it is a good starting point.

Hope, you enjoyed my instructable. And packraft is next.