We realized early on that the primary limitation of neoprene suits is the shrinking with depth. Ironically, that shrinking was ultimately connected with the flexibility of the suits, as the bubbled neoprene is a relatively soft thermally-resistive material because if the air bubbles.

We decided to tackle the thermal protection and flexibility separately. To make a material keep its thermal insulance with depth, we thought of using incompressible bubbles. Such bubbles could be supplied by hollow microspheres, which had been around for a long time, particularly for scientific applications. So, our basic idea was to encapsulate such microspheres in silicone, which is thermally curable, biologically inert, inexpensive, and reasonably flexible.

We researched the literature and discovered that the idea of hard hollow microspheres was not new. It turned out that there had been a couple of patents about that idea in the 1970s. Of course, our project started in 2016, which meant that those patents had long expired. We further found a technical report from 1972, prepared by the US Navy’s NCTRU in Natick, MA. The report indicated that the general idea of glass microspheres had been tried experimentally and had been shown to be effective, but the beads had tended to break and the NCTRU outfit had not been able to fabricate them sufficiently well.

In searching for commercial sources of microspheres, we were pleasantly surprised to find out that such hollow glass microspheres were easily and widely available from the 3M Corporation. These microspheres were already in commercial use, wherein they were mixed with paint and sprayed onto walls of buildings, to provide thermal protection. As a result, the microspheres were contemporarily mass produced at very low cost and good quality, which completely solved for us the fabrication problem that had stumped the NCTRU outfit in 1972.

So, we combined the commercially available K1 hollow glass microspheres from 3M with Sylgard 184 silicone from Corning. We solved the breaking problem that NCTRU had indicated, by mixing the microspheres with the prepolymer mixture in planetary mixers. These mixers act like a double centrifuge, wherein the sample is placed in a lidded jar, which is then rotated around its rotational symmetry axis that is tilted with respect to the vertical. Then the jar’s rotating assembly is itself rotated around a vertical axis. The result is a double rotation, which essentially sloshes the material around the jar, mixing it and degassing it at high rpm, but without the use of a beater. Because there is no beater, the mixing is much gentler mechanically, so the microspheres are not broken. This, together with the use of commercial beads produced at high quality and low price essentially solved both problems that had precluded NCTRU from further advances in the 1970s.

We characterized the material in terms of thermal insulance and then started building diver suits out of it. The ready suits were field-tested by diving and direct comparison with commercial suits worn under the same conditions.