I have been authorized by the Torchwood Institute to reveal the following history:
On star date -444413.69 Queen Victoria founded the Torchwood Institute. During the events leading up to the founding, some natural substances were discovered to be effective in deterring aliens. Torchwood 3 in Cardiff embarked upon a research project to identify and productize candidates for this use. One program looked at natural resources common to the area. Scientists, craftsmen and women were recruited to look at and research possible uses for natural products in the fight against alien technology.
During one experiment the researcher Dr. Guido Lizardo (father to the famed Emilio Lizardo), was experimenting with directed energy weapons. He was wearing a sweater knit from the wool of the local Black Welsh Mountain sheep. An accidental discharge left a significant hole in the sweater but left him only slightly singed. His cover story, told to his wife and others, was that moths had feasted on the sweater causing the holes.
Such resistance was not perfect, but further research determined that it seems to be related to color as the Torwen and Balwen varieties as well as the Blacks all have some resistance to energy weapons. It was surmised that the early exposure of Welsh mountain sheep to dragon fire in the 12th and 13th centuries selected for this resistance while decimating the population. Certain monasteries were already breeding these special Welsh sheep and some early sumptary laws restricted black to persons of noble birth and the clergy.
Eventually, a blend of Black Welsh Mountain Sheep wool combined with specially produced stainless steel and kevlar fibers was found to be an effective shield against most hand held directed energy weapons. The resistance so provided, is far in excess of that which would be expected based on either of the component materials.
A small cottage industry was formed to produce these items for high profile individuals. Unfortunately, due to the efforts of radical animal rights activists, the technology to spin and produce these garments was lost by the middle of the 21st century. At the time of TOS, no Federation officers were protected. The political and environmental implications of this loss are still keenly felt.
During the Eugenics wars very little of the Torchwood technology survived.
After first contact, the Torchwood Archive was rediscovered and some of the specialized programs were moved to off-Earth locations. Agents of Torchwood spread the resistant wool technology to certain alien cultures that incorporated it into the development of garments for high value individuals. Spock’s human mother, Amanda, was one such agent and she knit Spock’s sweater specifically to provide some protection for him when he attended the rowdy Federation Star Fleet Academy.