Ok before you start saying OP is retardzzz. I mean like How would you know... So it its not handblown? If its made in china they all look the same?
most of the pieces are still made by hand, but they are made quickly and they don't really care about how well made it is. Generally the problem is with china glass, not with things made in china. There could be some blowers in china making fantastic tubes, though I don't know of any. China glass is a lower quality of glass than the boro or pyrex used in nicer tubes, boro being generally considered the best. China glass is much more fragile, and also will degrade much faster with regular use. You can tell often just by looking...it will look poorly constructed compared to nicer tubes, the glass will feel light, and will often be thin in some areas, where nicer pieces are much closer to the same thickness throughout. Nicer glass also tends to resonate at a lower frequency, so if you tap on it, or even set it down nicer glass often has a much nicer, richer tone, where china glass will have a thin, higher pitched ring. (I'm a musician so I'm used to listening for things like that, other people may not be able to tell as easily)
mada, if I'm not mistaken I'm pretty sure Pyrex is just a brand name of borosilicate glass, similar to Schott Duran and others. I may be wrong though
I found this on wiki: Thus Pyrex can refer to either soda-lime glass or borosilicate glass when discussing kitchen glassware, while Pyrex, Bomex, Duran and Kimax all refer to borosilicate glass when discussing laboratory glassware. From what I understand it is a brand, but also can refer to a type of glass. I believe it is an alternative to schott boro glass made by a company called Corning... but I'm no expert on the topic.