Article of footwear having an upper incorporating a knitted component

1. An article of footwear having an upper and a sole structure secured to the upper, the upper comprising:

a knitted component formed of unitary knit construction, the knitted component including a first area and a second area, the first area including a first knitted layer and a second knitted layer that are at least partially coextensive with each other;

at least one tubular structure disposed on the first area of the knitted component, the at least one tubular structure comprising the first knitted layer and the second knitted layer that are overlapping and joined to each other along opposite edges to define sides of a tube;

a yarn having a configuration of a one-dimensional material, the yarn extending through at least a portion of a length of the tube;

wherein the tube formed by the first knitted layer and the second knitted layer has a unitary knit construction so as to be a one-piece element with the remaining portion of the knitted component;

wherein the second area of the knitted component is formed of unitary knit construction with the first area; and

wherein the second area has a higher knit density than the first area.

2. The article of footwear of claim 1 , wherein the knitted component defines a medial side of the upper, a lateral side of the upper, a heel region, and a forefoot region;

wherein the tube is disposed on one of the medial side and the lateral side; and

wherein the second area at least partially defines one of the heel region and the forefoot region.

3. The article of footwear of claim 2 , wherein the upper defines a throat between the medial side and the lateral side and a sole attachment area that is attached to the sole structure;

wherein the tube and the yarn extend generally between the throat and the sole attachment area;

wherein the second area at least partially defines the heel region;

wherein the knitted component further comprises a third area that is formed of unitary knit construction with the second area and the first area;

wherein the third area has a higher knit density than the first area; and wherein the

third area at least partially defines the forefoot region.

4. The article of footwear of claim 1 , wherein the second area of the knitted component includes an aperture; and

further comprising a lace that is received within the aperture.

5. The article of footwear of claim 1 , wherein the tube includes an end, and wherein the yarn exits the end of the tube to be partially external to the knitted component.

6. The article of footwear of claim 5 , wherein the yarn exits the end of the tube to form a loop; and

further comprising a lace that is received by the loop.

7. The article of footwear of claim 6 , wherein the at least one tubular structure includes a first tubular structure and a second tubular structure;

wherein the tube is a first tube defined by the first tubular structure;

further comprising a second tube defined by the second tubular structure; wherein the

yarn includes a first segment that is received within the first tube, a second segment that is received within the second tube, and an external segment that extends between the first segment and the second segment; and wherein the external segment defines the loop.

8. The article of footwear of claim 6 , wherein the knitted component includes an aperture adjacent to the end of the tube; and

wherein the lace is received by both the loop and the aperture.

9. The article of footwear of claim 8 , wherein the second area of the knitted component includes the aperture.

10. The article of footwear of claim 5 , wherein the yarn exits the tube and is secured to the sole structure.

11. An article of footwear having an upper and a sole structure secured to the upper, the upper comprising:

a knitted component formed of unitary knit construction, the knitted component having an outer surface and an inner surface that is opposite the outer surface; and

a yarn having a configuration of a one-dimensional material, at least a portion of the yarn being substantially enclosed within the knitted component between the outer surface and the inner surface;

wherein the knitted component includes a first area and a second area,

wherein the second area of the knitted component is formed of unitary knit construction with the first area, and wherein the second area has a higher knit density than the first area;

wherein the at least a portion of the yarn extends across the first area of the knitted component;

wherein the at least a portion of the yarn is spaced apart from the second area of the knitted component;

wherein the first area includes a first knitted layer and a second knitted layer that are at least partially coextensive with each other;

further comprising at least one tubular structure disposed on the first area of the knitted component, the at least one tubular structure comprising the first knitted layer and the second knitted layer that are overlapping and joined to each other along opposite edges to define sides of a tube;

wherein the tube formed by the first knitted layer and the second knitted layer has a unitary knit construction so as to be a one-piece element with the remaining portion of the knitted component;

wherein the first knitted layer at least partially defines the outer surface of the knitted component;

wherein the second knitted layer at least partially defines the inner surface of the knitted component; and

wherein the at least a portion of the yarn is received within the tube.

12. The article of footwear of claim 11 , wherein the yarn exits the tube to form a loop; and further comprising a lace that is received by the loop.

13. The article of footwear of claim 12 , wherein the at least one tubular structure includes a first tubular structure and a second tubular structure;

wherein the tube is a first tube defined by the first tubular structure;

further comprising a second tube defined by the second tubular structure; wherein the

yarn includes a first segment that is received within the first tube, a second segment that is received within the second tube, and an external segment that extends between the first segment and the second segment; and wherein the

external segment defines the loop.

14. The article of footwear of claim 12 , wherein the knitted component includes an aperture adjacent to the tube; and wherein the lace is received by both the loop and the aperture.

15. The article of footwear of claim 14 , wherein the second area of the knitted component includes the aperture.

16. The article of footwear of claim 11 , wherein an external segment of the yarn exits the tube and is secured to the sole structure.