SOLID 0.5% SILVER CONDUCTORS: Solid conductors eliminate strand-interaction distortion and reduce jitter. Solid silver-plated conductors are excellent for very high-frequency applications, like USB audio. These signals, being such a high frequency, travel almost exclusively on the surface of the conductor. As the surface is made of high-purity silver, the performance is very close to that of a solid silver cable, but priced much closer to solid copper cable. This is an incredibly cost effective way of manufacturing very high-quality USB cables.
FOAMED-POLYETHYLENE INSULATION: Any solid material adjacent to a conductor is actually part of an imperfect circuit. Wire insulation and circuit board materials all absorb energy (loss). Some of this energy is stored and then released as distortion. Forest USB uses air-filled Foamed-Polyethylene Insulation because air absorbs next to no energy and Polyethylene is low-loss and has a benign distortion profile. Thanks to all the air in Foamed-PE, it causes much less of the out-of-focus effect common to other materials.
TERMINATIONS: Precision gold-plated plugs are carefully attached with the very best solder. Through choice of flux and metallurgy, AQ solder has been optimized to make a low-distortion connection. The difference you hear between solders is a result of connection quality. AQ solder does not have a high silver content because the more silver there is in solder, the more difficult it is to make a good connection.