what material would you use to mate a mould of somethin so that you could make copies of something in fiberglass

Usually fibreglass itself - don't forget the mould release agent !

fibreglass matting, resin, hardener, honey wax, colour pigment/gelcoat, acetone, brush, roller. thats about it. oh, and the part you want to copy. ;)

 

http://www.resin-supplies.co.uk/

Edited September 22, 200817 yr by mario

Although, if you haven't got a part that you want to copy, i.e. you are making a new custom bit - MDF layered and shaped is best from what I've heard. I've also heard of rigid foam stuff being used.