ULS has scrim. You can see if if you really examine it closely, it will show up as a fine, thin weave inside the glass which is intended to provide cross se tonal support.
I hAve typically bought ULS. But this past summer I had a good conversation on with a long time bowyer that I respected very much. In that conversation he convinced me that the added scrim in ULS is not required as today's fiberglass is not prone to the longitudinal cracking of yesteryears glass. After reflecting, I would have to say that I never had a glass bow with UL glass crack.
I think from now on I will save the extra $ and just buy UL.