A low dielectric constant enables the use of (ultra) thin base materials for fast clocking speeds and increased packaging densities at current impedance levels. It is the low dielectric loss however, which turns high-speed digital into a success story: Signal traces can become longer, and power input can be reduced - both at improved signal integrity. Teflon™/glass fabric base materials can be laminated together with FR4 prepregs and FR4 inner layers for mixed dielectric multilayers. High-speed digital printed circuit boards are typically large-sized high-layer count multilayers. Until recently the unavailability of ultra-thin laminates and prepregs prevented single-component constructions. However RF-35P is a proven technological advancement which enables the manufacture of thinnest inner layers down to 50 micron (0.05 mm) thickness in production quantities. Based on this technology TacPrepreg TP-32 prepregs have been developed. The spec. details for RF-35P material you can find here.