A fiber-size composition contains a modified polyolefin, a hydrophilic coupling agent, and an enhancer with at least one of the following: a fluorine-containing compound, a hydrophobic coupling agent, a cyclic fatty acid, or at least two saturated fatty acids with at least one of said fatty acids having at least two acid groups. When reinforcing fiber materials sized with the composition are used to form composite articles, the articles show improved properties such as strength and color.