Are you talking about Raka's 5-ounce, which tests a bit stronger than the usual 6-ounce? If so, there are old threads about its wetout properties; some folks get good results, but some have had less clarity than with the usual 6-ounce or 4-ounce cloth. Try searching the archives for "5-ounce".
I used it on the hull of the boat I'm building now, and my experience was that I got a little air trapping as very fine bubbles along the stronger threads, a bit like fiberglassing ripstop; it's not prominent, but it is visible. I plan to use plain 6-ounce for the deck for that reason. In defense of the product, it's my first boat, and some of the more experienced folks do fine. It does seem reasonable to conclude that it's more demanding of technique and conditions to get a really clear wetout.

: I was ordering my glass cloth and was talked into 5oz vs 6oz, it sounded good
: over the phone. Is there any reason why I should not use the 5oz. My boat
: will be used in calm to moderate conditions, day and weekend trips, and I
: am about 175lbs.