The Stretch Fibre is a single layer soft cover. It is perfect in most conditions except damp areas. The stretch fibre cannot be 100% dust proof as you stretch the fabric you open the weave every time you pull the cover to stretch it over the car, they are approximately 90% dust proof and you would only notice any dust after a period of time.
Do not confuse this stretch fibre cover with others, it is more expensive for a reason, this is a 120g fabric and the cheaper options are much thinner offering even less dust protection. This is the heaviest fabric we can find to give flexibility and dust protection.