can i get away using a size small ul...
can i get away using a size small ul raincover or do i really need a medium?
The small would be too small for any ease of use if you could even get it on a loaded backpack. Especially if you were using the M or L version of this pack you would not be able to use the S raincover. I would definitely go with the M UL Raincover. The difference in weight between the two sizes of cover is minimal too. Osprey says it is a .25 oz difference.