Probably, as you suggested, foam particles.

Various foam gaskets are used to seal the joints in the ventilation ducts. Sounds like the foam has decayed.

Dash will have to come apart to repair if you choose to do so.

Steve

98 Contour SE Sport 2.5 Duratec ATX The wifey's car 89 Taurus SHO - 246K miles 94 SHO ATX - 190K 1997 F-150 5.4L ATX - The Workhorse 150K. ANY THREAD WITH "OMG" or "WTF" ETC IN THE TITLE WILL BE IGNORED!