Yes the moulds are made from flexible silicone rubber, I get the silicone and resin from
www.easycomposites.co.uk ok it's not cheap but it goes a long way, and I find it a fascinating extension to our hobby, I'm certainly not a master at it but it's really quite easy, just take some time making the fitting, fittings with a base such as bollard are the easiest, bond the fitting into a "box", I make the box out of styrene, mix the silicone and fill the box being careful to avoid air bubbles, when cured remove the sides of the box and remove the mould, depending on the fitting you can just flex the mould off others you need to cut the mould in half, it will then fit together and held with elastic band, mix the resin and fill the mould again avoiding air bubbles, that's it make as many as you want.