Ballistic Weave

The ballistic weave is an armor mod that allows improved defensive stats to certain clothing items, including outfits, clothing that can be worn under armor and a small number of hats.

This crafting ability can be learned from Tinker Tom after performing certain quests for the Railroad faction. Once this skill is learned, one can upgrade any applicable clothing item at an armor workbench.

Obtaining the skill
Progress through the initial Railroad faction quests until P.A.M. offers a series of minor Jackpot missions to secure DIA caches. These only become available after completing Boston After Dark and Mercer Safehouse.

After completing the first or second jackpot mission, Drummer Boy will tell the Sole Survivor that they need to speak to Tinker Tom, who will inform them about the ballistic fiber technology found in the DIA cache. At this point, the ballistic weave is unlocked at any armor workbench and Tom will sell some armored gear of his own.

Upgradable clothing
The following is a list of all clothing that can be upgraded, and if the item can either be worn underneath armor pieces or as a hat.

Bugs

 * Due to the dialogue flag setting, it is possible to miss the chance of learning this mod. Drummer Boy will keep saying that Tinker Tom wanted to see the Sole Survivor but Tinker Tom will not initiate the corresponding dialogue. Console command will fix this.
 * One may also get this mod without doing P.A.M.'s mission with the following console commands:
 * Acquiring the weave may become impossible if one has already finished the game with the Minutemen.
 * The clean black suit is supposed to be moddable, but is currently bugged in-game and prevents the player character from upgrading it on an armor workbench; the only solution for this is to use console commands. Tinker Tom may occasionally sell armored clean black suits, but these will only have the first level of ballistic weave and cannot be upgraded further.