Method of densifying porous articles

A method of densifying porous substrates using chemical vapour infiltration (“CVI”) in a CVI furnace, wherein the CVI furnace comprises a precursor gas preheating zone and a reaction chamber in which the porous substrates are densified, the CVI furnace comprising a bottom wall separating the precursor gas preheating zone and the reaction chamber, the bottom wall having a plurality of openings formed therethrough corresponding to a plurality of locations at which stacks of the porous substrates are positioned, the method of densifying comprising:

• arranging at least a first plurality of stacks of porous substrates in the reaction chamber, wherein stacks of porous substrates located at a periphery of the reaction chamber are undensified porous substrates, partially densified porous substrates, or a combination of undensified and partially densified porous substrates, and one or more stacks of partially densified substrates are located at a central location among the first plurality of stacks of porous substrates so that the porous substrates that are arranged at the periphery and at the central location of the reaction chamber have different densified states,
• and densifying the at least first plurality of stacks of porous substrates using a chemical vapour infiltration process.