Viton flouroelastomers have somewhat variable material properties. The following parameters are being used for eigenfrequency analysis.
Young's Modulus: 72,500-87,000 psi (cite: http://www.row-inc.com/pfa.html) *Accurate for PFAs
Poisson's Ratio: 0.48-0.50 (cite: http://www.engineeringtoolbox.com/poissons-ratio-d_1224.html) *Accurate for rubber
Density: 1800 kg/m^3 (cite: http://physics.nist.gov/cgi-bin/Star/compos.pl?matno=275)
The Young's Modulus for PFA turned out to be orders of magnitude greater than for Viton. The revised values produced much more accurate results:
Young's Modulus for Viton-75: 1950 psi or 6.6 MPa
(Courtesy Row, Inc. and Steve Vass)
This website contains other details: http://www.row-inc.com/viton.html