I do find that some fabrics are penetrable to bugs when stretched across the skin, e.g. at the elbows. I have seen this in the Montane Featherlite's Microlite fabric and the Pertex Quantum of the Marmot Ion. This hasn't been a significant problem, just a few pecks noticed here and there. I haven't had that same issue with the GoLite windshirts, but there are other trade-offs involved.