The chart that we link to below provides the thickness for a single ply (sheet) of each style of Pre-Preg after processing. These are grouped by the weight and type of the internal conductor layer (typical signal and plane layers) that they will be adjacent to (columns A-F). Those that are adjacent to the top and bottom copper layers will use the column designated for these (column G) regardless of the layer type. All plies that are not directly against a conductor layer (use for situations with more than 2 plies in an opening) will use the additional plies values (column H). These values are based on a minimum of 2 plies of pre-preg per opening between foil and cores or between cores.