About Water bottle and Thermos Flask:
Metal: Metal water bottles are more and more fashionable. Made primarily from stainless steel 304 or aluminium (aluminum), they are durable, retain less odor and taste from those plastic bottles, but can sometime impart a metallic taste. Metal water bottle and metal thermos flask are BPA free and very safe for use.
Howver, It is not recommended to fill aluminium water bottles with acidic liquids (e.g. orange juice), as this could cause aluminium to leach into the contents of the bottle. Depending on the type of source material and manufacturing process behind a stainless steel bottle, trace amounts of minerals can leach into contents from this type of bottle as well. Stainless steel bottles that do not contain a liner have been known to transfer a rusty taste and odor to contents. Bottles made with food-grade stainless steel grade 304, also known as do not transfer taste or odor.
Metal especially stainless steel water bottles and thermos flasks can be heavier than their plastic one. Single-walled metal water bottles readily transfer temperature of contents to external surfaces, which makes them unsuitable for use with unusually hot or cold liquids. Double-walled metal water bottles or known as thermos flasks are insulated to keep cold liquids cold and hot liquids hot, without the external surface being too hot or too cold. Because double-walled water bottles have more metal in them, they are more expensive. They are typically vacuum-insulated, but some may have a solid or gel insulation between the metal walls.