Max out your Boomers® experience with our Sub-Zero™ Boomers® series. GHS Sub-Zero™ Boomers® are Cryogenically treated in a computerized system with liquid nitrogen, taking them down to a temperature of minus 300 degrees Fahrenheit, and then gradually restoring them to room temperature. This treatment improves the dimensional stability of the strings, keeping them in tune, while increasing resistance to corrosion.