Some TOS collectors might be unaware that a special silver-speckled black fabric was employed in the fabrication of some of The Original Series Starfleet uniform pants. Below is a publicity photo of Ensign Chekov in which the fabric pattern is clearly visible.
The following pants were obtained directly from CBS/Paramount inventory and are believed to have been used in several episodes of TOS. It contains the speckled fabric at the cuffs only...Note the style of sewn-in costume label is identical to that used in the 2nd season Blue Federation dress photographed for an earlier post on this website and visible at the link: http://startrekpropauthority.blogspot.com/2008/03/special-photostudy-federation-sciences.html
Contrary to popular belief, these pants did contain pockets, however, the opening was aligned very high (almost right at the waistline) and would be easily hidden under the Starfleet tunic...
Note the TOS inventory designation P38.
A closeup of the speckled fabric ...
This second pair of pants contains speckled fabric throughout and clearly possesses some aged internal fabric and components.