Paulus,
What about Spectra? Does it hold water? or it is similiar to Dyneema in this?
About number specification of PE used in Japan
It is quite definite number, I think. At least, as far as it concerns known japanese makers starting from December 2010. There was a convention among line makers about PE which fixed rules of PE specification. They fixed that the certain number of PE must be equal to certain weight of the line in Denier units. 1 Denier equals to the case when 9000m of the material weighs 1g. If we transfer to grams, 9000m of PE6 must weigh 1080g, PE8 - 1440g, PE10 - 1800g. But the problem for us, users, remained unchanged. What's the point in knowing the line weight for a certain length, in case we still do not understand the actual diameter of PE to compare it between makers? May be, knowing the length, specific weight of the PE material and the actual weight of the length some specialistsl can calculate diameter somehow (not me), but I think it is still not clear for final user...
In approximately the same time they also fixed relation of the line number and its actual diameter in mm for nylon and flurocarbon lines. After that it must become more clear for the users. For example, #10 for nylon or fluorocarbon must be 0,52mm in dia for any maker and for both nylon and flurocarbon. I wish they made some similiar system for PE, but it must be very difficult due to the specific nature of PE material... So, such information which is placed on your site, Paulus, (actually measured diameters) is an absolute gold for anglers, I think. Thank you!