Cuben fiber vs silnylon

[Eugenemtbing]

Which is more waterproof, cuben fiber or silnylon?  I got a compression sack that I plan to mount on my bars for bike packing to carry my down sleeping bag and inflatable pad.  It's important that I keep the sleeping bag dry, and the compression sack is only water resistant.

I was thinking of sewing a silnylon "sock" dry bag of sorts that would slip into the compression sack and contain the down bag and pad.  Now that I have a little experience with cuben, I am wondering if there would be any advantages in using it instead of silnylon.

Does anyone have insights on this?

[12wheels]

It's always best to use two or more waterproof bags when carrying down bags or quilts.  I'd replace the water-resistant compression sack with a waterproof dry bag or compression sack and then make the inner bag out of the fabric that you're most comfortable working with because both can be made waterproof. 

[Adam Alphabet]

I've done some work with various weights of Cuben (0.51oz, 0.74oz, hybrid all from zpacks). I have never made anything with silnylon but have used it for years (stuff sacks, tarp, bivy bottom) until Cuben became more readily available.

I would use Cuben without hesitation, I find it very easy to work with. Unless cost is a concern or some stretch is desired in a project I don't see a point in using silnylon. In my opinion after using cuben, silnylon is kind of just 'second best'.

You could easily make something like this....
http://www.zpacks.com/accessories/dry_bags.shtml

I would do a 0.51oz roll top inner bag with no sewing, just bond all the seams. Then I would do the outer bag in 1.43oz or for greater durability cuben hybrid and you're golden.

These things work too as an outer bag, heavy for some peoples tastes but they work... http://www.seatosummit.com/products/display/1

[Eugenemtbing]

OK, I will use cuben.  It is easy to work with and seems incredibly tough (though not abrasion resistant). 

This is the bar bag I was thinking of using.  In the pics, it contains my sleeping bag, silk liner and Neoair pad, so it is a good size/shape for mounting on my bars.  Wonder if a standard dry bag would be better.

[12wheels]

Do you need a compression sack to reduce the diameter of the load?

[Eugenemtbing]

The down sleeping bag packs down well.  I was thinking compression sack to get things nice and snug on the bars, but a dry bag of the same size would do the same.

[Eugenemtbing]

Gen at Yama Mountain Gear had an interesting idea:  use turkey oven roasting bags for the final layer of water-repelling protection for a down sleeping bag and other similar gear.