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3D printing problem stringing

So these past few days I have been 3D printing again with my Ender 3 with PETG and 0.4 mm nozzle and while I have been using the same setting as usual I am seeing an unusual amount of stringing between the prints. Does anyone know why? If you're wondering regarding the settings here they are, I'm using Cura for slicing, see options:

Quality Shell Temperature Retraction Speed Cooling

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    $\begingroup$ PETG is just more stringy! Two things that pop out immediately; First: your perimeters are not bonding together, this may be caused by the under-extrusion you have set (90 % flow), you should always print with 100 % flow, also the temperature might be a bit low for PETG, I've printed kilometers of 2.85 mm PETG at 240-245 °C, but 1.75 mm may be printed at a lower temperature (heats up faster). Second, you have a lot of left over filament that collects at the printed outside perimeters, this may be caused by too much left over pressure. $\endgroup$
    – 0scar ♦
    Mar 22, 2020 at 14:11
  • $\begingroup$ I don't quite understand this point "Second, you have a lot of left over filament that collects at the printed outside perimeters, this may be caused by too much left over pressure", but for the temperature I already did try to print at 240-245 and it gets even worse, and for flow I tried at 100% and the stringing is reduced but it just ended up as blobs on the outside perimeters of the print. $\endgroup$
    – Brilliant Purnawan
    Mar 22, 2020 at 14:21

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The travel speed of 160 mm/s is a big red flag. PETG is not tolerant of a hot nozzle moving over it at high speeds, especially unretracted (combing). The nozzle will drag material in a stuttering pattern, every so often, marring the surface and pulling what it dug up into strings.

Lower the travel speed to the same as the print speed, and then experiment with whether you can increase it without problems. I would not try going over 80 mm/s and probably not even over 60.

For what it's worth, this sounds like softened/molten PETG is a non-newtonian fluid, where at low stress (slow moving nozzle pushing/pulling) it deforms gracefully, but at high stress (fast moving nozzle) it strongly resists deformation and has a discontinuous breaking point. A quick Googling turned up this article, Thermal, Rheological and Mechanical Properties of PETG/rPETG Blends, which might explain what's happening.

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Petg it stringy material, all I can do is keep it dry to prevent blob. but I live in hot country with high moisture so I decide to keep filament in heat dryer box while print. It help a lot.

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