Yeah, I know. It's not very effective as presented in CT. And it sounds dumb, as in "your armor ain't worth jack".
Recently I learned that there is a real, historical type of armor known as Jack. And it actually worked.
The CT definition of Jack (TTB, p. 43)
"A natural or synthetic leather jacket or body suit covering the torso and upper arms and legs. Jack is somewhat better than ordinary clothing or bare skin when defending against blades; it is worthless against guns."
Now read the definition of historical Jack:
Jack of Plate
"A jack of plate is a type of armour made up of small iron plates sewn between layers of felt and canvas. They were commonly referred to simply as a "jack" (although this could also refer to any outer garment). This type of armour was used by common Medieval European soldiers as well as by the rebel peasants known as Jacquerie. The present day equivalent is perhaps a bullet-proof vest.
The jack is similar to the brigandine. The main difference is in the method of construction: a brigandine is riveted whereas a jack is sewn. Jacks of plate were created by stitching as many as 1000 small overlapping squares of iron between two canvases. The garments weighed about 17 pounds (7.7 kg), which made them much more acceptable to the wearer than solid breastplates. They also offered a tactical advantage: they allowed soldiers to rest the butts of weapons firmly against their shoulders, which wasn't feasible with smooth-surfaced plate armours. Jacks were often made from recycled pieces of older plate armor, including damaged brigandines and cuirasses cut into small squares."
The real explanation of Jack sounds much more like Traveller's definition of Mesh armor. Also, the description given would put Jack of Plate at TL2, not TL1.
How to fit Jack of Plate into the TTB combat matrices? Like this:
Jack of Plate is Mesh+1. That is, 1 worse than regular Mesh against all weapon types. Available at TL 2, cost is 300 Cr.
Image source: Wikimedia Commons