Ceramic matrix composites and their preforms

A preform comprising:

• a first sub-laminate comprising a first plurality of first layers;
• where at least one layer of the first plurality of first layers comprises a first spacing between successive first tows that is different from a second spacing between successive second tows in an adjacent first layer;
• wherein the first sub-laminate has a first average pore size;
• and
• a second sub-laminate comprising a second plurality of second layers;
• where each layer of the second plurality of second layers has a third spacing between successive tows;
• wherein the second sub-laminate has a second average pore size that is less than the first average pore size;
• and wherein at least one of the first sub-laminate or the second sub-laminate has at least two gradients in porosity that have opposing slopes;
• wherein the first sub-laminate contacts the second sub-laminate;
• and wherein a warp tow from the first sub-laminate penetrates the second sub-laminate or vice versa.

A preform comprising:

• a first region comprising one or more first sub-laminates;
• wherein the one or more first sub-laminates comprise a first gradient in average pore size along a first cross-section of the preform;
• where the first cross-section of the preform is located in the first region;
• and
• a second region, wherein the second region contacts the first region;
• and wherein the second region comprises one of more second sub-laminates;
• wherein the one or more second sub-laminates comprise a second gradient in average pore size along a second cross-section of the preform;
• where the second gradient in average pore size is different from the first gradient in average pore size;
• where the first region has a different thickness from the second region;
• where the second cross-section is located at the second region and wherein the second region is not the same as the first region;
• wherein the first sub-laminate contacts the second sub-laminate;
• and wherein a warp tow from the first sub-laminate penetrates the second sub-laminate or vice versa.