This is usually a sizing or fit issue rather than a faulty product.
Pack covers are cut to suit a specific pack capacity range, so a cover that's too large for your pack won't cinch down tightly enough to stay put in wind, while one that's too small won't fully seat over the pack.
Make sure you're using the size matched to your pack's litre capacity, tuck any loose straps and hip belt away before fitting the cover, and use the drawcord/toggle to cinch it firmly around the base of the pack rather than leaving it loose.
Articles in this section
- My pack cover keeps blowing off or letting water in around the edges - what am I doing wrong?
- How do I stop my tarp poncho flapping around in windy conditions?
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- What's the difference between a pack cover and a poncho for rain protection?
- Are Sea to Summit head nets treated with chemical repellent, or is protection purely physical?