From the Dampit website:
The original humidifier for string instruments, Dampit has been protecting wood instruments for over 40 years. Invented and patented in 1966 by profesional violinist and composer Ralph Hollander, the Dampit has protected the instruments of thousands of musicians worldwide.
Long-lasting and easy to use, the Dampit is made of the finest materials. With proper care, your Dampit will give you years of good service without needing frequent replacement.