Reading about the original bed, they only claim that it is suitable for PLA and it is not rated for temperatures above 70C as you would want to use with PETG. Descriptions vary. It may be polycarbonate.
I bought a PEI build plate for use with PETG and set the original Ender plate aside for the time being. PEI is Polyetherimide by the way. PEI is recommended for PETG and is supposed to be equally good for PLA.
The one I have is made/sold by "hictop" and is golden colored. It is also rigid. It cost me about $30. The texture looks exactly like my original Ender. They actually send a magnetic slab with an adhesive bottom that you could install on your printer, but my Ender 3 Pro already has a magnetic bed so this is not needed.
I had some trouble initially, but washed it thoroughly twice with water and dish detergent, releveled it, and now it seems just fine. Given the need for the bed to be super clean, it makes sense to avoid touching the surface with fingers (which always carry grease and oils). For various reasons it is often recommended not to clean the bed with alcohol when it is hot.
I had some warping, but raised the bed temperature from 70 to 80, turned off my air conditioner during the print to avoid drafts, reduced the fan to 50 and got perfect results. Using 245 on the print head for PETG.
My friend Dave says he prints with PETG on a glass bed at 70C using a light spray of aqua net hair spray and it all works great.
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