This is due to the capillary action of the bead allowing gravity to draw any moisture present down the inner surface of the outer leaf to drain away at foundation level.
Cavity wall insulation beads leaking.
The problem is that doing this properly injecting the glue with the beads takes about 3 times longer than installing the beads alone.
The bonding agent creates a stable continuous layer within the cavity preventing any movement or sagging of the insulation over time and also any loss of bead if the walls are drilled at a later date.
The problem is that this fills the cavity with a material that can allow water to cross the cavity causing dampness and if the material is not evenly distributed cold spots where insulation is missing can attract condensation.
Similarly if your cavity walls were wrongly insulated this could cause you problems down the line.
Cavity wall insulation beads will not allow dampness or moisture to penetrate the cavity in a properly constructed wall.
When beads are injected into the cavity wall they are injected with a upvc glue which binds all the beads together.
Eps expanded polystyrene beads and polyurethane foam are the most commonly used these days and with good reason.
Plumbing pipes and leaks copper water pipes in the wall are usually secure but occasionally one may develop pinhole leaks and spray enough water to cause insulation problems.