This may seem like a simple one. But it happened to me a time or two back when I was starting. It may only seem like just one little thread of peel ply, but it is enough to cause a vacuum leak. A stray strand of carbon or fiberglass can have the same effect. It will allows the vacuum to pull air in and leave voids in your laminate. Under vacuum bagging conditions, it may not be terrible, but it is much more detrimental to an infusion, especially if its a long run from this stray fiber to the vacuum port. The second part of this is why large flanges on your mold are nice. In this picture my mold is an old mirror I had laying around. The haze on it is the over spray of the spray tack I used to hold the layers together so don’t mind that. The flat panel I was making was just about as large as the mirror so I was working very close to the gum tape. This increases the chance of a stray fiber landing on the gum tape. Now a days I’m well aware of it, but in the beginning when I wasn’t as aware, I would sometimes just go right over these strays and wonder why I would have a little trail of bubbles across a part sometimes. I now try and make the flanges on my molds extra large, usually in the 6″ beyond the part range. This also allows a nice resin break. So just something to keep an eye on to lessen the chance of voids.