I just bought a pair of the Rynoskin pants, which are a very light, tightly woven nylon/lycra blend, base layer designed to keep insects from biting you without chemicals.
Sunday morning, I did 2 hours at a local preserve wearing shorts with those Rynoskin tights underneath to protect my legs - but mostly to see if they are hot to wear in the summer.
They are not hot to wear in the summer. Since they are thin and ultra light, the sweat evaporates just as quickly (if not more so) as it would from bare legs.
They claim 99.x percent effective against biting insects including ticks, fleas, and biting flies. On my 2 hour walk, I was bitten on the calf by 4 horseflies. Through the Rynoskin pants.
I'm still going to wear them in a couple weeks when I go up for my next section, but they will have been treated with permethrin. I sweat too much for applications of insect repellent to be reliable.