Described in certain aspects are composite extracellular matrix material products including expanded collagenous materials in combination with non-expanded collagenous materials. Methods for their preparation and use are also disclosed. Certain expanded collagenous materials can be prepared by treating a first collagenous material with an alkaline substance under conditions effective to expand the first collagenous material, and recovering the expanded material. Expanded materials can exhibit beneficial persistence and tissue generation characteristics when implanted, and can be used in the formation of highly porous medical implant bodies which can be compressed to fractions of their original volume and will thereafter substantially recover their original volume.