Lowtech Graph lists low-tech options for every need of a home. Here you can compare them, find tutorials to build them, and link them together into a circular system. Why low-tech?
Stores heat and gives it back later. Moves heat in TIME rather than reducing the total, which is why a mass row is never a substitute for an insulation row.
Ranked by volumetric heat capacity, how much heat a given volume of the material stores for each degree it warms. Water holds roughly twice as much per unit volume as masonry, which is why a water wall out-performs an equivalent thickness of stone; the trade-off is that masonry is usually structure you already have, while water needs a sealed vessel.