According to Kelley and also stated by Alex Pang, Kelley designed the first mousepad a year later, in 1969.

Optical mice have the problem of not working well on transparent or reflective surfaces (such as glass or highly polished wood). These surfaces, which often include desk and table surfaces, cause jitter and loss of tracking on the display pointer as the mouse moves over these reflective spots. The use of mousepads with precision surfaces eliminates spot jitter effects of modern optical mice.

Mouse Pads