Commercial spandex can be prepared with greater efficiency, improved consistency and at lower costs from a high-solids content polyurethaneurea polymer solution. The polyurethaneurea is prepared using a combination of 4,4′-MDI and 2,4′-MDI, and an amount of chain extenders and chain terminators such that the polymer solution, prior to spinning, is highly soluble and has an appropriate pre-spun IV and primary amine content. Such spandex fibers, and the fabrics and garments comprising them, have good dyeability and colorfastness, as well as other desirable characteristics.