According to Wikipedia, permethrin is also useful as a single-application topical remedy for scabies. The much-maligned ivermectin requires two doses some time apart for equal effect. Huh. And it does mention the US and UK are both impregnating uniforms with permethrin.
Any idea how old your gear is? I'd like to now how good that is long-term. There's a commercial spray-on product suggesting 6 weeks or 6 washings, but an impregnated fabric would presumably be more effective long-term, and the instructions there might be more about selling bottles that a real decrease in effectiveness.
It was probably ten years old when I discovered that. When I was trying to find out more about it I came across some DoD regs that require it to last for the life of the uniform which they equated to 50 washings. Even after that it supposedly only losses effectiveness slowly. When I noticed it with my BDUs it was well past the 50 washings mark, so it seems that's likely to be true. It's definitely more effective than the spray-on stuff, that's why the DoD made the switch.