http://www.rtpcompany.com/info/guide/resistance.htm (http://www.rtpcompany.com/info/guide/resistance.htm)
http://www.goodfellow.com/csp/active/gfMaterialInfo.csp?text=%2AP&MATID=ES30&material=1 (http://www.goodfellow.com/csp/active/gfMaterialInfo.csp?text=%2AP&MATID=ES30&material=1)