Passive systems rely on heat-driven convection or heat pipes to circulate water or heating fluid in the system. Passive solar water heating systems cost less and have extremely low or no maintenance, but the efficiency of a passive system is significantly lower than that of an active system.
316L Stainless Steel. 316L Stainless Steel is commonly used for jewelry because with it will not oxidize nor turn black with only minimal maintenance. Its resistance to corrosion and staining, as well as its durability and sleek look have made stainless steel body jewelry the most popular type of material for piercing enthusiasts worldwide. Our body jewelry products are made with high quality 316L Surgical Steel which is safe for all types of body piercings or implants.
Unlike aluminum, stainless steel will need no liner to keep you safe and healthy, so look for smooth metal inside your bottle. You can still find an insulated stainless steel water bottle; just make sure the inner liner is also stainless steel.