Don't you love (or hate) those crazy Japanese product names?
Ok, it's a bow string material (ludicrously expensive) which I thought I'd try.
Damn, I got the string a tad short, the stuff just doesn't stretch at all. A Dacron string which appears too short is generally just right as it will stretch a bit as it's shot in and will require some twisting to shorten it again. But this stuff just doesn't shift at all, it twangs with a much higher note than the Dacron.
The traditional bowyers Bible says that it is faster because you can make the string of fewer strands and thus lighter and it's the reduced mass which increases the speed.
Irritatingly, the string has zero information with it and the manufacturers website isn't much better, merely recomending a thread count for recurves or compounds.... hmm maybe they don't shoot longbow in Japan, and maybe their Yumi bows have traditional silk strings?
Anyhow I made a 10 strand string which I thought was going to be long enough, but it gives me a bracing height about 1/2" over my fistimelle (That's a fist with the thumb raised like a 'thumbs up' sign which is the traditional measure for a longbow bracing height... very handy).
I've fettled the nocks a bit which has brought it down a whisker but I'm not really happy, so I'll make another string. I can re-use the material from the first string on a shorter bow as it's so expensive. (Over £30 for a reel about half the size of a reel of Dacron which is about £8).
I havn't shot it as a fully finished string yet so I can't really say if I can feel the difference.
Re-making the string made me realise that I needed some sort of jig to hold the string under tension whilst I was serving it (serving is the whipping applied to protect the nock ends and centre section of the string). 
I had a long piece of 2x2" which I'd made into a portable tillering rig which I used last Monday, so I added some bits to that to hold the string.
Most effective, a length of rubber strap provides the tension and the string is held by winding it in the manner of a cleat.
The string is first wound between two nails to form a long skein, lttle tabs of masking tape keep the two sides separate, the ends are tied. One of the 'sides' is whipped for about 2", the ends of the wipping are then folded over to meet each other and form a loop, bothe sides are then wipped together for the main body of the string.
Thus you can see there are half as many strands in the loop as there are in the main body, a few extra strands are added at the loops before serving for extra strength and to bulk up the string a little so it doesn't cut into the nock so much.
Ok, it's a bow string material (ludicrously expensive) which I thought I'd try.
Damn, I got the string a tad short, the stuff just doesn't stretch at all. A Dacron string which appears too short is generally just right as it will stretch a bit as it's shot in and will require some twisting to shorten it again. But this stuff just doesn't shift at all, it twangs with a much higher note than the Dacron.
The traditional bowyers Bible says that it is faster because you can make the string of fewer strands and thus lighter and it's the reduced mass which increases the speed.
Irritatingly, the string has zero information with it and the manufacturers website isn't much better, merely recomending a thread count for recurves or compounds.... hmm maybe they don't shoot longbow in Japan, and maybe their Yumi bows have traditional silk strings?
Anyhow I made a 10 strand string which I thought was going to be long enough, but it gives me a bracing height about 1/2" over my fistimelle (That's a fist with the thumb raised like a 'thumbs up' sign which is the traditional measure for a longbow bracing height... very handy).
I've fettled the nocks a bit which has brought it down a whisker but I'm not really happy, so I'll make another string. I can re-use the material from the first string on a shorter bow as it's so expensive. (Over £30 for a reel about half the size of a reel of Dacron which is about £8).
I havn't shot it as a fully finished string yet so I can't really say if I can feel the difference.
Re-making the string made me realise that I needed some sort of jig to hold the string under tension whilst I was serving it (serving is the whipping applied to protect the nock ends and centre section of the string). 
I had a long piece of 2x2" which I'd made into a portable tillering rig which I used last Monday, so I added some bits to that to hold the string.Most effective, a length of rubber strap provides the tension and the string is held by winding it in the manner of a cleat.
The string is first wound between two nails to form a long skein, lttle tabs of masking tape keep the two sides separate, the ends are tied. One of the 'sides' is whipped for about 2", the ends of the wipping are then folded over to meet each other and form a loop, bothe sides are then wipped together for the main body of the string.
Thus you can see there are half as many strands in the loop as there are in the main body, a few extra strands are added at the loops before serving for extra strength and to bulk up the string a little so it doesn't cut into the nock so much.
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