I posted here about 4 months ago when I bottled a few pints of porter in these:
The gym I belong to goes through a steady amount of these, so they're easily come by on a daily basis. The bottles that interest me are listed as 18 and 22 oz., and most have had the "Speed Stack" product in them.
The bottles are #1, I assume PETE.
The bottles are opaque, unlike a lot of beverage bottles.
Although the product isn't carbonated, the bottles are very sturdily constructed, with a large cap that makes for easy pouring.
My trial bottling of several of the 18 oz. size was completely successful. They endured bottle conditioning, a thousand mile airplane ride in my suitcase (inside a gallon Ziploc bag to be safe) with no trace of a leak. When they were opened and poured, they showed carbonation & head commensurate with those bottled in 9" longnecks.
I've about got enough for a batch, so I'm going to put something dark in there again. Even though the test bottles were soaked in PBW and sprayed with Star San, they still retained the aroma of the beverage. Since this aroma was not detectable whatsoever in the finished porter, I'm going ahead with a full batch.
NB: Please, no questions as to WHY I'm doing this. Yes, I have bottles, of several different types. No, I don't mind capping. I'm just doing it because I want to......and because if this works out, these will be nearly ideal travel containers.