Compared to alginate, reversible hydrocolloid impression materials are:

Reversible hydrocolloid impression materials are indeed better for undercut areas when compared to alginate. This is primarily due to the physical properties of reversible hydrocolloids, which allow them to be more adaptable to the contours of the dental structures during the setting process. They offer a significant degree of detail reproduction and can capture fine anatomical features, including undercuts, more effectively.

One of the key characteristics of reversible hydrocolloids is their ability to undergo phase changes. They can transition from a gel to a sol state when heated, making them easier to handle in terms of placement and removal from the mouth. This flexibility during the initial setting phase allows them to flow into spaces that might be more challenging for alginate to capture.

In contrast, alginate, while commonly used for impressions, can be less effective in scenarios with significant undercuts because it may not adapt as closely to the details of the tooth or tissue surfaces when it sets. As a result, while both materials have their own set of advantages, reversible hydrocolloid is typically favored for capturing detailed impressions in complex anatomical areas.