In a recent study tests were conducted to establish the level of vacuum (or negative pressure) that is created inside the leading brands of drinking cups.

This indicates the strength of the negative pressure that your child will have to overcome to create a flow of liquid. The stronger this negative pressure, the harder it is for your child to drink.

Strong vacuum inside drinking cups causes discomfort for infants, forcing them to suck unnaturally hard. Therefore wherever possible it is better to use drinking vessels that do not have high vacuum levels.