Are they glass as described? Or, as they appear, and per comment, are they really cheap plastic? Thermal tumblers are not usually glass.
Are they really made from borosilicate glass, as per the description? Or, as they appear in the picture, and per the single comment, are they really just cheap plastic? Thin cross-section thermal tumblers are not usually made from glass. Pyrex is an example of borosilicate glass products. This type of glass has an ability to withstand thermal shock, and tolerates microwave and diswasher quite well. That material would make these quite nice.
6 years, 6 months ago