Ballistic Weave is one of the most useful and valuable armor mods you can get in Fallout 4, but it's not a mod you can just buy from a vendor.
FALLOUT 4: How to Get the BALLISTIC WEAVE Armor Mod in Fallout 4! (Highest MAXIMUM Damage Resistance)
In Fallout 4, you have a full suite of upgrades and enhancements you can apply to your armor pieces, but Ballistic Weave is one of the few armor mods that can actually improve the outfits and clothing underneath your armor. Ballistic Weave increases both the damage resistance and energy resistance of just about any outfit or piece of clothing, including unique items. And the higher your Armorer skill, the more effective the mod is.
There are a few obstacles to overcome and missions to complete to get your hands on Ballistic Weave, but it's almost certainly worth it.
Players can learn how to use the Ballistic Weave armor mod from Tinker Tom, the railroad's supplies and repairs expert, provided they complete a number of missions in a row.