Invisible Zipper or Concealed Zipper comes in 3 weights: #2, #4, #6. The coil is 2mm, 4mm or 6mm across the closed zipper coil.
2mm: Best in light weight fabrics, dresses that aren't very tight.
4mm: Use in medium weight fabrics for pillows, duvet covers, garments.
6mm: This is heavy duty for use in tight garments (wedding gowns), pillows in heavy upholstery fabrics, slipcovers. Some manufacturers call this "#5 Invisible". My pulls will still open & close this, just a bit tighter.
Pulls on Tape: The Elves in the warehouse put the pulls on the tape for you. $1.20 per pull which includes labor & the pull.
Pulls NOT on Tape: YOU put the pulls on to make the zipper tape open & close.
I have been testing this weight of invisible zippers in cushions and in the backs of slipcovers for years. Even though this is heavy duty, there are still the limitations that you have with all invisible zippers. They don't take as much stress as a standard coil zipper. To take the stress off the zipper when closing, I make sure that I pull the zipper tape together prior to trying to zip it up. And yes, this means it takes 2 people to zip a bride into her dress!