Yes, I should have said 'or similar product'

I have no idea what they are made of but they all seem to come under the heading of 'weatherproof sealants' - can be used in damp conditions, paintable with most paints - resists mould growth' so it doesn't sound anything like silicone.

Mind you I've used plenty of silicone products that claim to be mould resistant and they should be done under the sales description act.