Okay, with a little more research I found out that both are made of 30D nylon fabric (not silnylon), with silicone coating and 100% USA made. SO seams are triple stitched, not sure about Kifaru. Also, one more feature that I forgot to mention regarding SO is, for their tipi's, they have additional tie out loops that are placed a couple feet above the base and around the perimeter of the shelter to be used for additional guy lines for heavy winds or the tipi's can be brought down and staked out at that level, decreasing the height and footprint, as conditions dictate.
This is off of Kifaru's website:
FABRIC: I want to be clear on one thing - what our material is NOT. It is not what everybody else is using. It is not silnylon, and it certainly isn't in the same category. Silnylon--either sourced from offshore or domestically--has less than half the tear strength of our proprietary fabric. Yet our fabric is just as light. The only thing silnylon has going for it is that it's far cheaper than our stuff. This fact means our shelters cost more.
I took this off of another forum where Kevin (SO part owner), was comparing the material that Kifaru uses and the material Seek uses.
Both are american made 30D nylon with silicone coatings. Our choice came down to being able to consistantly meet a certain waterproof rating where the other fabric provided could not do that.