• Polyurethane-Casting-Resin.html http://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/casting-resin/Xencast-PX90-Semi-Flexible-
• Speed of sound in rubber-based materials for ultrasonic phantoms https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5126009/

polymeric materials include neoprene, ethylene propylene diene monomer (EPDM) and polyurethane rubbers

• http://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/casting-resin/Xencast-PX30-Soft-Flexible-Polyurethane-Rubber.html
• http://www.ondacorp.com/images/Rubbers.pdf
• http://www.acousticpolymers.co.uk/pages/profile.html

• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3651250/ or 10.1118/1.4802083

• Loved Nasa: @done add to un0rick

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ice40 again at https://www.element14.com/community/thread/43876/l/project-icestorm-fully-open-source-fpga-tools-for-lattice-ice40?displayFullThread=true