A twin neck bottle (also sometimes called a “dual‐chamber bottle”, “Bettix bottle”, or “twin-mouth bottle”) is a specialized container with two neck openings / chambers: One chamber is for bulk storage of the liquid. The other (smaller) chamber is a built-in measuring or dosing chamber — you squeeze or otherwise transfer fluid from the storage chamber into the dosing chamber, then pour from that dosing chamber. They are commonly made from HDPE (High‐Density Polyethylene) for chemical resistance, translucency, durability.