Hands down Cuben fiber is the material of choice. Just make sure when constructing the tarp not too go too thin. There are several weights ranging from .3oz and up. You may want to the lightest possible but I would suggest at least the 0.48oz or higher to provide durability. Also, be careful when putting the tarp together, I don't know if you've worked with Cuben fiber before, but you can't just sew it and call it a day. The fabric will simply tear. You need to tape it. Truthfully, I don't think Cuben fiber is worth it. Silnylon is light/durable/cheap enough for me (plus it is easier to work with and more readily available). Good luck!