Sulde is not the name of an object. It is a word for something closer to vital force, the presiding spirit or animating power of a person, a lineage or a people, and the standard is called a sulde because it is where that power is held. Getting this the wrong way round produces the common mistranslation of the sulde as a flag, and a flag is precisely what it is not. A flag represents. A sulde houses.
The physical form is a shaft, wooden or metal, topped by a broad disc or a spearhead, with the tail hair of stallions hung in a skirt from the rim so that it moves in wind. Mongol tradition distinguishes a white standard of nine tails, associated with peacetime and with the state, from a black standard associated with war, and both are attached to Chinggis Khan in the tradition.
Because a sulde holds something, it is attended rather than stored. Responsibility for that attendance falls to named people, and the standards are brought out, dressed, offered to and returned rather than displayed continuously. That is a materially different relationship from the one a nation has with its flag, and it survives into the present arrangement in Mongolia, where the nine white standards are state property and are also, unambiguously, treated as what they are.