R-Value has been by far the single most misleading metric of insulation performance to date, more so in today's modern building's insulation as Jay and Bill pointed out. If your good technically check out the "Breathable Walls"
thread and the three different modes of moisture transport, Permeability, Absorption/Desorption (or drying speeds based on water content of air or Relative Humidity) Equilibrium Moisture Content (EMC) is part of this metric), and Capillary absorption/desorption. Most modern world manufactures do not disclose this data.
Two schools are highly insulated envelopes or high mass, or hybrids. Other two are loose fill in cavities such as fiberglass, cellulose, mineral wool.....Because FG is very loose and test have shown it's r-value drops significantly when moist "convective loops" or "air barries" enter the cavity and circulated in and out of it, a new school was developed to "air seal" the cavity to stop the loops. Cellulose industry took the test further and determined that dense pack prevented the loops, eliminating or reducing the need for air sealing or the need for a drying direction, proposes sealed vaulted roofs and walls I do not agree with. As you pack in insulation (I think the two values are 3 and 5 PCF if I remember right) the R-Value goes down, bridging goes up, drying speeds down, If drying does not occur in less than 48 hours mold can develop IF there is a food source (plastic interface would me one, most glues in laminated plywood, so are the admixes in most
concrete).. So it is VERY dependent on the installer to verify density and mating materials. I think 3 PCF is better IF it is verified and does not settle to create air barriers which lower effective or whole wall r-values. Many manufactures list nominal r-values from lab test that mislead. Cellulose does dry fast if it has a "Breathable" assemble, it has a perm rating of ~23....Wood across the grain is slow, along fast same with hemp, flax, wool fast tightly pack good at reducing loops high perm 41, very low MC....plywood slow, plastic and foam barrier n/a off the charts slow and wrong in most cases.
Mass designs incorporate a binder that binds to most everything it touches such as clay-slip, limecretes, mag-cretes, etc....combined with hemp, straw, wood chips, that create air pockets or r-values and hygroscopic properties, dry very fast, capillary breaks such as neoprene under sills are not needed, make excellent cast in place over studs (double is good to have something to nail to for cabinets, etc, timbers, at the surface) but it can get pricey, lots of mortar mixing and shoveling in. Most have r-values in the range of 1.5/inch to 3.5/inch such as hemp-crete (12 inch) u-value test out of the UK show. Strawbale is up there with clay or lime plasters, especially to the interior. Again, highly misleading since "dynamic mass effect" out performs r-value in most cases, especially at managing moisture it's value is not reduced by. It can drop heating and cooling loads by 2/3 especially in passive
solar designs to net zero as Jay said, So can Rammed Earth, most insulation's cannot unless there is large air seal effort to blower door test below .6 ACH Passivhaus. With mass two systems are resonating at different frequencies if you will, the outer surface and inner......Most high insulation design do not have such a assembly property that functions at depths from 1-3 in from both surfaces, storing-releasing heat and moisture, but never bridge if designed right. Drying occurs in both directions from radiant heat that constantly changes small air per hour but does not effect heating and cooling loads or loose it to the outside.
Cellulose - depends on the configuration. Straw tubes behave different than packed cellulose, or solid wood tube grains depending on directions, or bound hemp, straw, chips, etc.
My .02
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Here they must be mixed and colored from scratch which doesn't make them cost effective for most building professionals.
