Lab circulators and water baths incubate, warm, and cool samples slowly by surrounding the sample in temperature-controlled water. Circulators and baths hold water or another fluid and heat or cool the fluid to the desired temperature. The sample is placed into the bath and left in place until it reaches the bath temperature. Circulators have a pump that moves water around the sample to maintain even temperatures and speed processing. Water baths don't have a pump, so they're generally smaller and quieter than circulators. Bath fluids and accessories help maintain uniform temperatures.