Both are thermistors. Both change resistance with temperature. That’s usually where the similarity ends — and mixing them up in a design leads to a part that does the opposite of what you needed.

Opposite behavior, by definition

The names describe the direction of change: PTC (Positive Temperature Coefficient) resistance rises as temperature rises. NTC (Negative Temperature Coefficient) resistance falls as temperature rises. That single difference in slope is why the two components end up in almost entirely different roles in a circuit.

What each one is used for

Why they aren’t interchangeable

An NTC’s smooth, continuous curve makes it easy to convert a resistance reading back into an accurate temperature value — exactly what you want from a sensor. But that same smooth curve means an NTC has no natural point where it “shuts itself off,” so it can’t self-limit as a heater the way a PTC element does.

A PTC element’s sharp, near-step change at the Curie point is precisely what makes it a poor general-purpose sensor — you get high resolution only in the narrow band around the transition, not the smooth reading across a wide range that sensing applications need.

Choosing between them starts with the question you’re asking

• Need to generate heat and have it self-limit without external control? → PTC
• Need to measure temperature accurately across a range? → NTC
• Need overcurrent protection that resets itself once current drops? → PTC (used as a resettable fuse)

If your project needs the heating side of that list, our guide to choosing a PTC heater architecture covers how to match liquid, air, cased, or chip-form elements to your mounting and thermal requirements.