http://usmilitary.about.com/cs/army/a/armygrooming_3.htm
http://www.army.mil/usapa/epubs/pdf/r670_1.pdf
pg 4-5
(3) Female haircuts will conform to the following standards.
(a) Females will ensure their hair is neatly groomed, that the length and bulk of the hair are not excessive, and that the hair does not present a ragged, unkempt, or extreme appearance. Likewise, trendy styles that result in shaved portions of the scalp (other than the neckline) or designs cut into the hair are prohibited. Females may wear braids and cornrows as long as the braided style is conservative, the braids and cornrows lie snugly on the head, and any hairholding devices comply with the standards in 1–8a(3) (d) below. Dreadlocks (unkempt, twisted, matted individual parts
of hair) are prohibited in uniform or in civilian clothes on duty. Hair will not fall over the eyebrows or extend below the bottom edge of the collar at any time during normal activity or when standing in formation. Long hair that falls naturally below the bottom edge of the collar, to include braids, will be neatly and inconspicuously fastened or pinned,so no free-hanging hair is visible. This includes styles worn with the physical fitness uniform/improved physical fitness uniform (PFU/IPFU).
(b) Styles that are lopsided or distinctly unbalanced are prohibited. Ponytails, pigtails, or braids that are not secured to the head (allowing hair to hang freely), widely spaced individual hanging locks, and other extreme styles that protrude from the head are prohibited. Extensions, weaves, wigs, and hairpieces are authorized; however, these additions must have the same general appearance as the individual’s natural hair. Additionally, any wigs, extensions, hairpieces, or weaves must comply with the grooming policies set forth in this paragraph.
(c) Females will ensure that hairstyles do not interfere with proper wear of military headgear and protective masks or equipment at any time (see 1–8a(1)(a), above). When headgear is worn, the hair will not extend below the bottom edge of the front of the headgear, nor will it extend below the bottom edge of the collar.
(d) Hair-holding devices are authorized only for the purpose of securing the hair. Soldiers will not place hairholding devices in the hair for decorative purposes. All hair-holding devices must be plain and of a color as close to the soldier’s hair as is possible or clear. Authorized devices include, but are not limited to, small, plain scrunchies (elastic hair bands covered with material), barrettes, combs, pins, clips, rubber bands, and hair bands. Devices that are conspicuous, excessive, or decorative are prohibited. Some examples of prohibited devices include, but are not limited to, large, lacy scrunchies; beads, bows, or claw clips; clips, pins, or barrettes with butterflies, flowers, sparkles, gems, or scalloped edges; and bows made from hairpieces.
(e) Soldiers may not wear hairnets unless they are required for health or safety reasons, or in the performance of duties (such as those of a cook). No other type of hair covering is authorized in lieu of the hairnet. The commander will provide the hairnet to the soldier at no cost.