Nylon, Copolymer and PVDF are more dense than water, but often they will not sink due to the effect of the surface film, especially in a flat calm. There are several ways to overcome this, the most common being to degrease the hook length by pulling it through a putty like mixture of Fuller's Earth, washing up liquid and glycerine. You can buy this under the brand name of "Ledasink".
Even this stuff is not 100% in it's effect, due I think to minute quantities of oil that is realeased by certain insects when they eclode (hatch). Such oil release causes a phenominom called a "wind lane". To beat this and get your line to sink, get a smidgin, and I mean a smidgin, of Kryston Heavy Metal and roll it between your forefinger and thumb onto the hooklength about 18 inches away from your hook/fly. This has the effect of causing your hooklength to break through the surface film when it falls.
Try this and see if it does not increase your catches.