What is the best way to open your flip-top caps?

Moulded into the rim of the collar (the bit that fixes onto the tube) are a couple of small ridges which serve to prevent the cap from coming open accidentally. When trying to open the tube, any pressure that pushes the cap against these ridges actually serves to lock it shut, thus making it almost impossible to open.

To avoid this, we have found that by using the index finger to apply pressure to the back of the cap just above the hinge, and at the same time sliding the thumb up the indentation on the collar to the cap generally opens the tubes easily and quickly. This sounds more difficult than it really is and can normally be done with just one hand.