Type I collagen is explored heavily for use in biomaterials, but the role of other extracellular matrix components in regulating collagen organization is gaining attention. We show that as the ratio of type III to type I collagen increases, fibril diameter decreases. A mixture of the two collagen types results in a more open structural network, corresponding to a more compliant material, as compared to a material composed of only one collagen type. Glycosaminoglycans also affect collagen organization and tissue properties. We show that chondroitin sulfate decreases the collagen fibril diameter. Additionally, chondroitin sulfate (CS) increases the void space of a collagen I or collagen III gel, resulting in a more compliant material, but the interactions between types I and III collagen negate the effects of CS. The simple combination of these components results in materials with unique structural, mechanical, and biological cues that can be useful in tailoring biomaterials for tissue engineering.