Opening or poor seams occur when the seams of the wallpaper spring or open during the drying process. This can be as little as part of 1 millimeter, to 1 to 2 millimeters.
THERE IS NOTHING IN ANY WALLCOVERING THAT WILL MAKE OR CAUSE THE SEAMS TO OPEN.
There are many reasons for seams to open during the drying process of the wallpaper.
All wallcoverings that have paper as their web or base will expand and relax once wetted, but during the drying process will rely very heavily on the preparation of the substrate to have been carried out correctly to hold the wallpaper in place, and not allow the product to move or open.
Not that 'paste the wall' wallcoverings do not expand and show seams when sheets are aligned correctly, although the usual wall preparation is still recommended.
OPEN OR POOR SEAMS CAN BE CAUSED BY THE INSTALLER
1. Not sanding with the correct grit sandpaper or not sanding at all.
2. Not dusting the entire surface, to remove all dust particles.
3. Not glue sizing the entire surface, so as to seal off the porosity of that surface.
4. Stretching the product during installation.
5. Force drying the product, either by putting a heater in the room, or a dehumidifier, or by the heat of the sun coming into a room during, or even after, installation.
a. Surface not glue sized at all
b. Incorrect paste
c. Paste too thin
d. Incorrect use of seam roller ( i.e too much pressure applied, causing the paste to be pushed out of the seams).
ALL THESE FACTORS CAN, AND DO, HAVE A BEARING ON WHETHER THE SEAMS WILL OPEN DURING THE DRYING PROCESS.