Permethrin is a synthetic insecticide based on pyrethroids from chrysanthemum plants. It is a dyable substance that loosely bonds with a lot of clothing: nylon, cotton, wool, and others. It does NOT bond to siliconized tents, recycled PET(fleece), and many plastics that do not pick up water. It may or may not “stick” to your pack…depends on the material. It won’t do any good on your tent if your tent is waterproof.
Dipping, in higher concentrations or for longer time, is much more effective than spraying. Spraying will last through 6-8 washings on the right material.
It is highly toxic to aquatic life and cats. Fish, amphibians, and insects are targeted by interrupting their nerves. It does NOT break down in a sewage plant. Do NOT pour it on the ground. Any excess you do not use should be placed in a wide pan and exposed to UV (the sun) for several hours to destroy it. It can get into the water table, lakes and rivers if you just dump it.
It is generally safe for humans. The military has been using it for many years. Some people (<1%) are allergic to it.
Dip it for about an hour in a 1% solution.
Hang to dry.
Rinse the excess out, treating the rinse water the same as the original mixture.
Dipping on nylon pants, for example, will last for a couple years. It will stay through about 50 normal washings.
Once it in your cloths, it will NOT leach out in rain, during stream crossings or laundering. Eventually it will, but 50 washings is nearly half the lifetime of your cloths. If you set aside a special set of hiking cloths, well treated, it may last much longer. I have a set about 6 years old that still protects against bugs.
A certain saturation is reached with each material. You cannot add more, because it just washes out. This will vary with the material.
The past few years, on longer trips, I often pick up fleas/chiggers in my sleeping bag. I plan on doing my sleeping cloths/long johns, but generally you do not do your socks and underwear. I have not had a tick in over 10 years using Permethrin, despite hiking through some known problem areas. I assume it works. You really cannot tell, because insects will avoid it. It works with blackflies, mosquitoes, deerflies, horseflies, spiders, ticks, etc. Like anything else, there is a risk using a toxic substance. I think that risk is offset by the potential for diseases transmitted by the bugs. Make your own decision.
Usually, you can get 5% or 10% Permethrin on line as an agricultural insecticide. They may make stronger versions, but I never tried them. The spray on, for some reason, does not seem to bond that well with clothing based on the manufacturers spec. I agree, it washes out easily.
Note that some heavily dyed clothing will NOT pick up very much. The "bonding" sites are already bonded. Lighter colors are usually easier to treat. Remember to UV all waste. Mosquitoes can bite through loosly woven tops. They will not live, but I think of it as REVENGE!