I recently got my new Osprey Atmos 65, and I really want to attach some patches that I bought online. Will normal iron patches work or can I sew them on instead?
Will it damage the backpack?
Be very careful of iron-on - nylon melts! You have to get the temperature right. I wouldn't be confident that the patch would hold as the rucksack flexes, though I guess that depends on the quality of the adhesive you use.
Sewing will puncture the fabric and allow a little moisture through. You could mitigate this by applying silicone seam sealant to your stitch-holes on the inside of the pack. Not a bad solution, and less prone to disaster than iron-on.
If the patch is made of nylon, you could bond it on for a reliable solution.
This will only work reliably with nylon. If the patch is polyester or some natural fabric you'd probably be better to sew it on and seal the holes.