Distributed air-gap powder cores (Iron Powder, MPP, High Flux, and Kool Mu) exhibit soft saturation. This is different than sharp saturation that is found in ferrites and laminated materials. A diagram of soft saturation vs. sharp saturation is provided below.
Soft saturation protects an inductor designer from a fault condition where a large in-rush of current saturates the core and drops the inductance of the inductor from near 95% of initial inductance to almost no inductance. Based on this risk, a designer must design far enough away from the “knee” of this sharp curve to avoid having an inductor to saturate. Another concern is that materials that exhibit sharp saturation curves also are affected by temperature. The sharp saturation curve will shift to the left as temperature of the core increases.
Soft saturation allows the designer to design an inductor anywhere on the soft saturation curve. This is commonly referred to as a DC Bias Curve in Magnetics catalogs. Optimally, a designer should ensure that at peak currents, the inductor is operating at no less than 50% of initial inductance. Distributed air-gap cores are not affected by temperature as much as ferrites or other sharp saturation materials. A rise in temperature of the core does not result in a drastic shift in the soft saturation curve.