Elongate, flexible catheter includes a shaft having a proximal end, a distal end, and a lumen extending therein. The shaft has an inner layer comprising an amorphous polyamide having a Shore D durometer value of greater than 78, and an outer layer comprising a semi-crystalline polyamide or copolyamide having a Shore D durometer value of less than 76. The outer layer is thinner than the inner layer. The shaft has an increased resistance to kinking as compared to a similar shaft of a single layer of the amorphous polyamide having a Shore D durometer value of greater than 78.