+ For 1,5 weeks I use the shell now for my 25-liter messenger bag (shoulder bag). Through the two elastic straps with snap that keeps well. + The shell does what it is intended, the yellow is very striking and the two reflectors strips reflect extremely well. (The printed silver arrows do not reflect.) Whether it is waterproof, I can not say yet. + One can shake up the envelope and cram into the small mesh pocket sewn. I think that's better than a storage bag. - To a filled 35 or even 40 liters backpack fits the shell definitely not. Therefore, a star deduction. For backpacks and shoulder bags up. 25 liter can recommend it though! ADDENDUM: Already after 4 weeks use the seam has risen slightly in the rubber. But since then it rips a not. All in all a quite useful, but also worthy of improvement articles. (3 stars)