End users can confirm with the manufacturer as to a presence or lack of binder in the backing material. Most major suppliers of knitted reinforcements are providing binderless chopped strand backed knits. The chopped strand backing is held in place by the bias yarns. Backing adds an additional layer within the knit which must be wet-out and lastly backing retards the ability of the knit to shear which effects the overall conformability and draping qualities of the knit. Unlike woven reinforcements, knits have little to no fiber crimp.
Fiber crimp retains resin and resists resin drain-out.
To avoid drain-out issues thixotropic fillers may be added to the resin mix prior to wetting out. Thixotropes increase a resin's resistance to sag or drain. In other words the resin will wet into the knit and then resists draining until it is cured. We have spent a little bit of time looking at the loading ratio of thixotropic fillers. The following represents a guideline used by one of our customers who uses quite a bit of knitted reinforcements.