From the OES website
Prices and weights include stuff sack and seam sealing (where appropriate). Compare that to other tarp manufacturers, who force you to seam seal your own tarp and make your own stuff sack, but donít include these factors in their final weights.
I just noticed the optional seam sealing for $6.50. I don't believe it was an option when I bought both of my tarps, it was just part of the price.