Cytoplasmic abundant heat soluble (CAHS) proteins are highly expressed in response to desiccation. There are two hypotheses for their function in tardigrades. The vitrification hypothesis is the idea that, when a tardigrade becomes desiccated, the viscosity within its cells increases to the point that denaturation and membrane fusion in proteins would stop. A second hypothesis, the water replacement hypothesis, posits that CAHS proteins replace water in other desiccation-sensitive proteins, protecting the hydrogen bonds normally reliant on water. CAHS proteins are dispersed throughout the cell in normal conditions, but form a network of filaments during environmentally stressful conditions. This network transforms the cytoplasm into a gel-like matrix and prevents the cell from collapsing as water leaches out. This state is reversible and the proteins disaggregate when exposed to less stressful conditions.
When forming the filament network, CAHS proteins have long helical domains that interact in a coiled manner with each other. These interactions are possible due to the proteins' partial disorder, with two flexible tails surrounding the helical domains.
CAHS proteins have been studied to observe their interactions with trehalose, a sugar used by other species to prevent desiccation. Trehalose was found to interact at higher levels with CAHS proteins than other sugars such as sucrose. However, the exact functions of trehalose inside tardigrade cells are still unknown.