Limp, floppy, flaccid, flabby, flimsy, sleazy mean deficient in firmness of texture, substance, or structure and therefore unable to keep a shape or in shape.
Limp applies to something that lacks or has lost the stiffness or firmness necessary to keep it from drooping or losing its original sturdiness or freshness.
Floppy applies to something that sags or hangs limply.
Flaccid implies a loss or lack of elasticity or resilience and therefore an incapacity to return to an original shape or condition or to keep a desired shape; the term applies primarily to flesh and other living tissues. In extended use the term implies lack of force or energy or substance.
Flabby applies to something that is so soft that it yields readily to the touch or is easily shaken. In extended use the term implies the loss or lack of what keeps a thing up or in good sound condition; it often carries suggestions of spinelessness, spiritlessness, or lethargy.
Flimsy applies to something that by its looseness of structure or insubstantiality of texture cannot hold up under use or strain. In extended use the term applies to whatever is so frail or slight as to be without value or endurance.
Sleazy applies especially to flimsy textiles, but it often suggests, as flimsy need not, fraud or carelessness in its manufacture. In extended use the term may stress lack or inferiority of standards or inferiority of the resultant product, but often its suggestion is one of cheap shabby inferiority.