Indwelling catheters are held in place by a small balloon at the top of the catheter. This is inflated and sits firmly in the urethra. Balloon catheters are always 2-way catheters. One channel is used to inflate the balloon and the second to drain the urine. If there is another channel for flushing solutions, they are called 3-way catheters.
The tips of the catheters can be straight (Nelaton tip) or curved (Tiemann tip) and have one or two so-called eyes. The eyes are the openings of the catheter through which the urine is drained. Ready-to-use catheters are already coated with a lubricant so that they can be inserted directly without pretreatment.