Hi Sona, The answer to you question is that dielectric constant is the measure of how good of an electrical insulator a material is. The lower the number the better the insulating properties of a material. The higher the number the better a material is at conducting electric current. From this spec it looks like you can use standard garden variety FR-4 Regards, Scott Kramer Sales Engineer ThermalWorks, Inc. 714 Adams Avenue, Suite 209 Huntington Beach, CA. 92648 Tel. +1 (714) 960-5152 x203 ----- Original Message ----- From: Fineline Circuits, Inc. To: [log in to unmask] Sent: Friday, May 03, 2002 10:04 AM Subject: [TN] Dielectric Constants For Core and Prepreg Hi For a 4 layer pcb with .062 overall thickness, what does it mean when the specifications call out for "Dielectric Constant for core & prepeg (e) 4.3min to 5.3 max. Thanks for your help. Sona Sitapara Fineline Circuits Inc. (215) 364-3311 [log in to unmask]