P/00/0 11 Regulation 3.2 AUSTRALIA Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT ORIGINAL TO BE COMPLETED BY APPLICANT Name of Applicant: Esoniee International Co., Ltd. Actual Inventor(s): Yu-Ju Huang Address for Service: A.P.T. Patent and Trade Mark Attorneys PO Box 222, Mitcham, SA 5062 Invention Title: Three dimensional pad structure for a bra The following statement is a full description of this invention, including the best method of performing it known to me/us:- THREE DIMENSIONAL PAD STRUCTURE FOR A BRA BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a bra, and more particularly to a three dimensional pad structure for a bra. Description of the Prior Art Nowadays, there are normally two ways of breast enhancement, besides plastic surgery, the most common method is to improve the structure of the bra. For example, the methods for improving the structure of the bra 1 is to insert bra pads 10 which are made of water bag or silicon, as shown in Figs. 1-3, or to insert massage protrusions or cups in the bra, namely, the inserted pads or cups are used to push up the breast, making the breast look more large and stand out. However, the above methods have some disadvantages. Take the water bag as example, the water bag is likely to break if it is too heavy or inappropriately manufactured. The elasticity of the silicon pads is not very good and will become even worse after being washed with water. As far as the massage protrusions are concerned, the problems might be caused that if the massage protrusions are too large, the wearers might get hurt and feel uncomfortable, and if the massage protrusions are too small, they hardly have any influence to the breast. SUMMARY OF THE INVENTION The primary object of the present invention is to provide a three dimensional pad structure for a bra which is formed with a hollow space in each of the pads, and air can selectively flow into the hollow space. When the pads are 2 compressed, the hollow space will disappear, turning the pads into a flat shape. Once the pressure disappears, the pads return back to original inflated state in which the hollow space appears again. Through such repeated inflation and compression of the pads, the bra has a better wearing comfort and makes the breast stand out more and look more real. To achieve the above object, a three dimensional pad structure for a bra in accordance with the present invention comprises a plurality pads between an inner fabric layer and an outer fabric layer of a bra, the pads are characterized in that: each of the pads including a first layer and a second layer superposed with each other, and a hollow space being left between the first and second layers so that air is allowed to flow into the hollow space, when the pads are compressed, the hollow space will disappear, turning the pads into a flat shape, and once pressure disappears, the pads return back to original inflated state in which the hollow space is formed again. Another characteristic of the present invention is that in order for the bra to has better shape and provide better support, it can insert at least one assistant pad in the hollow space, so that the hollow space is reduced to an appropriate extent, which helps reduce the difference before and after the pads are compressed, improving the wearing comfort of the bra. Yet another characteristic of the present invention is that the first and second layers each include a first piece and a second piece, conjunctions of the first pieces and the second pieces are formed as arc-shaped connecting edges, and a highest point of the inflated hollow space defined by the first and second layers is located at the arc-shaped connecting edges. 3 BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is an exploded view of a conventional bra; Fig. 2 is a perspective view of the conventional bra; Fig. 3 is an illustrative view showing that the conventional bra is worn on the wearer's breast; Fig. 4 is a perspective view of a bra in accordance with the present invention; Fig. 5 is an amplified exploded view of a part of the bra in accordance with the present invention; Fig. 6 is an amplified assembly view of a part of the bra in accordance with the present invention; Fig. 7 is an exploded view of the first and second layers of the pad of the bra in accordance with the present invention; Fig. 8 is a perspective view of the pad of the bra in accordance with the present invention; and Fig. 9 is a perspective view of the pad of the bra in accordance with another embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to Figs. 4-8, a bra 2 in accordance with the present invention comprises two connected cups 21 and two back straps 22 extending backward from outer periphery of the two cups 21. Each of the back straps 22 is provided with a locking member 23 at one end thereof for connecting the two back straps 22 to each other. Each of the back straps 22 is connected to a shoulder strap 24 in such a 4 manner that each of the shoulder straps 24 has an end fixed to the edge of the respective back straps 22. At the lower edge of each of the cups 21 is inserted a pad 3 which is located between an inner fabric layer 211 and the outer fabric layer (not shown) of each of the cups 21 of the bra 2, when the bra is worn, the pads 3 can push up the breast. To ensure that the pads 3 have an optimal elasticity, as shown in Figs. 5 and 8, each of the pads 3 consists of a first layer 31 and a second layer 32 superposed with each other in such a manner that a hollow space 33 is left between the first and second layers 31, 32, and air can flow through the first and second layers 31, 32 into the hollow space 33. In normal conditions (the bra is not pressed), with the support of the first and second layers 31, 32 and the air contained in the hollow space 33, the pad 3 can be maintained in an inflated state. When inserted in the cups 21, the pads 3 will be pressed by breast, and the air will thus be pushed out of the hollow space 33, so that the pads 3 are brought into a compressed state and become flat. However, once the pressure from the breast disappears, the first and second layers 31, 32 will restore their original shapes due to their elastic properties, meanwhile air will come into the hollow space 33 again, and thus each of the pads 3 returns back to its original inflated state in which the hollow space 33 is formed again. Through such repeated inflation and compression of the pads 30, the bra has a better wearing comfort and makes the breast stand out more and look more real. The forming of the hollow space 33 of the pads is described as follows. As shown in Figs. 5, 7 and 8, the first and second layers 31, 32 each include a first piece 311, 321 and a second piece 312, 322. The conjunction of the first piece 311, 321 5 and the second piece 312, 322 is formed as an arc-shaped connecting edge 313, 314, 323 and 324. In this embodiment, the first piece 311, 321 and the second piece 312, 322 are connected to each other by sewing, and the highest point of the inflated hollow space 33 defined by the first and second layers 31, 32 is located at the arc-shaped connecting edges 313, 314, 323 and 324. It is noted that in order for the pads 3 to have inflated height variation, it can change the arc-shaped connecting edges 313, 314, 323 and 324 of the first and second pieces 311, 321, 312, 322, in other words, changing the size of the arc-shaped connecting edges 313, 314, 323 and 324 of the first and second pieces 311, 321, 312, 322 can obtain different inflated heights of the pads 3 for fitting (the inflated height refers to the height of the pads 3 when the pads are in an inflated state), so as to meet different wearers' needs. Referring to Fig. 9, in order for the bra 2 to has better shape and provide better support, it can insert at least one assistant pad 4 (there are two assistant pads in this embodiment) in the hollow space 33, so that the hollow space 33 is reduced to an appropriate extent, which helps reduce the difference before and after the pads are compressed (preventing the difference from becoming too large), improving the wearing comfort of the bra. To summarize, the three dimensional pad structure for a bra in accordance with the present invention is formed with a hollow space in each of the pads, and air can selectively flow into the hollow space. When the pads are compressed, the hollow space will disappear, turning the pads into a flat shape. Once the pressure disappears, the pads return back to original inflated state in which the hollow space appears again. Through such repeated inflation and compression of the pads, the bra 6 has a better wearing comfort and makes the breast stand out more and look more real. 7