Paul,

It is possible to make your own air holding amas as the example suggests. If you plan to use a sewing machine, then that tool will apply to the outer skin of an ama of this type and then it would have an inner, air holding bladder, typically made of glued, or RF welded, urethane. (Needle holes are a nightmare for sealing reasons)

This build technique is used with great success by AIRE rafts and kayaks. While it does weigh more than other build methods, it also provides a durable outer skin (mostly done with 32 oz. and heavier, PVC impregnated polyester fabric) it also gives you the option of having that additional puncture resistant layer outside the air holding bladder.

You can get urethane impregnated fabrics which are very good at holding air. You can also get PVC impregnated fabrics which do the same thing. From these types of fabrics, you can have a single skin, air holding bladder with the exterior being tugh enough to withsatnd any expected puncture inducing scenarios.

Anticipate what kinds of conditions in which the flotation ama will be subjected during its service life and work with the build method (and fabric) that will give you that performance at the price point you can afford.

Most prototypes are built with PVC imnpregnated fabric because it is the least expensive. Some stay at that price point and others go on to produce their production goods in uretahne impregnated material as it can be RF welded quickly and effciently. This is especially true if the form can be doen in a two part, RF press style mold.

It's moderately expensive to tool-up for this application (relative) but it eventually yields finished parts that are very price competitive in the long run.