into the pattern shown in fig1 18 by starting with a sheet of high yield strength material such as stainless steel with a thickness that is equal to the reduced thickness portions 128 of sheet 122 and folding over sections of the sheet of material against itself by stamping or otherwise forming the material folding the sections of the sheet creates full thickness portions 126 where the material is folded over against itself and creates holes 130 where the material is displaced during the folding process the sheets 122 and 124 are combined into composite sheet 120 composite sheet 120 has generally planar upper and lower surfaces 121 and 123 fig1 sheet 124 is formed in a manner similar to that of sheet 122 except the material is a high thermal conductivity material such as copper and holes 136 are created by folding material from the holes 136 over to create the full thickness portions 132 after the patterns are formed into sheets 122 and 124 the sheets are positioned as shown in fig1 and then combined as shown in fig1 into the composite sheet 120 as before the full thickness portions 126 of the steel have a high yield strength that resists.