Is there a question here?

What slicer do you use? What are your brim settings, and initial/1st layer settings? 1st layer height, extrusion width?

Why is bed temperature so low? PETG is normally recommended with 80-85C bed. With a lower temperature the PETG will cool and shrink a little, breaking adhesion with the bed, making the corners peel up/warp.

A thick first layer is good, like your .3mm. Is your first layer squished together right, or can you see little spaces between the lines? When my Z height is a little high, the brim is worthless, because the lines didn’t properly adhere to the other lines in the brim or the model.

What is your extrusion width for the first layer? I do mine fat, 150% to 200% over nozzle size, so everything squishes together, and adhesion ends up being good, Z height a little less temperamental.

I've used 75C bed with 235C nozzle on PETG with no problems -- try a little glue stick and a hotter bed.

I use a glue stick with PETG because without it PETG sticks so well to the build surface that it rips hoes in it. I don't run the bed at 75 °C or above because of heat creep, even with fans running in the enclosure and the door open. Also the fan on the head sink is the fastest rpm I could find. The only thing else I could do is not use an all metal hot end.

"The only thing else I could do is not use an all metal hot end." Weren't you one of the people who told me I didn't need an all metal hot end? Install the captive Capricorn PTFE in the heat break, and you can run a conventional hot end up to 300 C.

@ChinchillaWafers My first layer extrusion width is set to 200%. What would probably help is to get some overlap in the first layer extrusions. How about bridge flow ratio?

So far the only way I know to cause more first layer overlap is to decrease the initial z height.

@ZeissIkon: That is very bad advice. A (modified?) PTFE tube designed for high temperatures might be ok to operate up to 260 but definitely not 300.

@ChinchillaWafers: PETG does not need extreme bed temperatures. On an unheated bed the first lines have some trouble adhering, but once things do adhere, PETG adheres too well if anything. I normally use 40˚C for PETG now. PETG is one of the lowest-warping materials you can print.

@R.. GitHub agree PETG is a forgiving, low shrink plastic, but the filament comes with a recommendation for bed temp, probably 75-80C, and from the photos no one could claim Perry is not having problems with warp. I’ve had tall narrow parts peel up like his, you still have to use all of the tricks to keep it stuck down, and highest bed adhesion for any material is at its glass temperature. Doesn’t mean it won’t stick adequately at a lower temperature, just not as well.

In my experience, the reason for recommending high temperatures is that, if the bed is too cold and has nontrivial heat conductivity, it will leech the heat out of the part while you're trying to bond the second layer to the first layer, making the first layer peel off the bottom after the print is finished. I haven't encountered warping. But I suppose it might help to try a higher temperature.

Personally from a standpoint of warping, I like layer N to be cooled so much that it won't futher contract from cooling before I put layer N+1 on top of it. If the lower layers are kept hot for the whole print, they'll try to warp at the end when you finally cool down the bed to take it off, and only the structure of the layers on top of them is there to prevent it. This means you may get warping dependent on the geometry of the part (what constraining forces the upper layers provide) and your final part has strong internal stresses in it.

@PerryWebb: They're useful if you want to print materials that need high temperatures, or print "normal" materials at extreme speeds (lots of the #speedboatrace folks print ABS at 275+). Otherwise, they're just more complex to get right than a PTFE-lined one.

@R..GitHubSTOPHELPINGICE "A (modified?) PTFE tube designed for high temperatures might be ok to operate up to 260 but definitely not 300." I'm only repeating the claim Capricorn makes for their tubing, that it can be run up to 300C the same way normal PTFE can be run up to 250C.

@ZeissIkon: Does Capricorn actually make that claim? I only recall seeing it in the listings an Amazon and such that are almost surely counterfeit Capricorn anyway, and didn't think they made any of their own claims about the real thing.

Hmm. I have a Capricorn branded kit -- 2 m of tube, cutter, four couplers (two each thread size) and some labels and such -- that was sold as rated for 300 C. Did I buy counterfeit? smile.amazon.com/dp/…

@R..GitHubSTOPHELPINGICE Okay, I found where the advertisers (probably value-added resellers, providing short lengths plus accessories and packaging) get the 300C figure: captubes.com/safety.html#temps shows 300 at the top of the "maybe" range. The 260C you cited is the top of the "yes" range, I read this chart to say you can print at 300 with good ventilation and potentially shortened tube life.