I had an email a couple of days ago from a guy I know who works within the fishing line industry, and below is what he wrote. I asked his permission to copy and paste his words into this blog post, and he kindly said yes, but would I please keep his name and company name out of it. I thought this might be of interest and also help clear up a bit of the rubbish that is so often talked about fishing lines by people who quite frankly don’t have much of a clue about the technical ins and outs of it. This guy does, and it makes for some interesting reading. Have a read of my blog post here that this guy kindly emailed me about - many thanks ********** for sending me this info and for allowing me to put it up here. I love it when my blog works like this and helps me (and I hope you) understand certain things more clearly.
“Extruding nylon lines - most sport fishing line is extruded using similar machinery, some of it new, some of it old, some well maintained and some not. This all affects the consistency of the process. At ******* we extrude to +/- 6% of diameter/breaking strain before rejecting a batch. This means that although the average variance might only be 2% or so it could be up to 6% in certain sections - ****** are not special in this regard and 6% is pretty much an industry standard. So your 15lb line could anywhere between 14.1 and 15.9lb at its weakest/strongest point.”
“Testing - there are two industry standard test but unfortunately they are from the wrong industry! In textile testing (and unfortunately nylon filaments fall into this group) then the tests are a straight pull to break test without a knot (tensile strength) and pull to break with a single overhand knot in the middle of a dry line (knot strength). Both our these are useless for anglers - tensile strength can never be achieved because you need a knot to fish, and knot strength is unrealistic because 99% of anglers use a better knot than a single overhand in the middle of the line. In addition there is another problem with the tests. You've seen the machine and it is a steady pull to break - no impact. Again, hardly a realistic fishing scenario.”
“Standards - I am not sure about other countries but in Europe the consumer standards authorities use the tensile test when checking companies and allow tolerance of +/- 10% on diameter and breaking strain. There were a few cases of prosecutions in France and that led to EFFTA introducing the Line Charter (http://www.eftta.co.uk/line-charter/) to try and clean up the industry. Although it has flaws it is clear and they have had good sign up to it.”
“Culture - In the UK historically people bought line by breaking strain, and only in more recent times have anglers started to consider diameter in a more important way. If you are going to buy a 15lb line then you want a strong one, and you may remember an old brand called Sylcast that was famous for being exceptionally strong. In reality it wasn't, it was just thicker and so stronger than stated. Europeans by contrast have looked at diameters when buying for a lot longer than we have. So again as a way of getting ahead of the competition it makes sense to have your 0.35mm stronger than the rest as nylon is nylon and there is not a great deal you can do except cheat and state a higher breaking strain than the reality. Interestingly the US has always sold line by "lb test" ratings. The rationale being that a 15lb Test will always break at a minimum of 15lb with a knot. Like the UK this encourages companies to put heavier line on the spool to make their "15lb test" stronger than the rest. There is some IGFA rated line where it cannot break at more than 15lb (although interestingly the IGFA strength testing standard is much closer to a fishing scenario than the industry standard).”
“So in answer to your question "Are the ratings on a spool of line essentially a load of rubbish?" then the answer is yes. If the line is from a EFTTA Line Charter member than you can be sure the diameter and breaking strain is correct in the laboratory, but a bit overstated for real fishing scenarios. If it is not Line Charter certified then it could be greatly overstated (Poland and Italy being the worse offenders) or greatly understated (probably a UK brand).”
“Outside of fishing the filament industry discusses filament strength in terms of gram per denier. It's a kind of strength by diameter basis that ignores the material and the fibre diameter and gives a gauge with which to compare differing fibres. I once did some testing and compiled data for a bunch of nylon lines to compare the grams per denier. In that attached file you can see the results. If you check the grams per denier column you can see the best lines achieve about 12 , and the worst about 6. That's what you can achieve with nylon and anyone claiming more than 12 grams per denier for a nylon line is lying. (and for comparison Aramid (Kevlar) lines are around 20-25 grams per denier and HPPE (Dyneema/Spectra) around 35 grams per denier).”