Water beading

When you first have your convertible hood weatherproofed, the hydrophobic coating cause water to bead up into little droplets, many of which will roll off your hood, keeping it dry.

However, after a period of a few months, this effect will reduce until it no longer happens. This is perfectly normal and there is nothing to worry about, the fabric is still waterproof. What happens is that dust and dirt gets onto the fabric, and this breaks the surface tension of the beads of water. What then happens is the was soaks through, but not into the hood. You should still find that if you place your hand on the hood, it is mostly dry.

You can tell if the weatherproof coating has worn off because the water soaks into the fabric, so when you touch it, it is sopping wet. At this point, you should get it re-weatherproofed as if it is impregnated with dirt, grit and organic material, and is sopping wet, this provides an ideal medium for moss and fungus to grow.

Additionally, you don't need to worry about water soaking through the fabric layer, as this is just cosmetic. There is a waterproof layer of neoprene beneath it which prevents water ingress.