These are the slides from my DesignCon 2010 presentation, created with my partners Don DeGroot, Sanjeev Gupta and Colin Warwick. We look at how the frequency dependent material properties are described so that they remain causal and what the impact is. We show that not including the frequency dependent dielectric properties may result in too optimistic a simulation of eye opening for long traces at 5 Gbps or short traces for 10 Gbps and above. If you are confused about causal material models, this lecture is for you. See also the written paper BTS115.