Hi ShopperGirl,
You are getting into some rather technical issues here that can be very complex and somewhat counterintuitive which is the relationship between ILD, resiliency, hysteresis (energy absorption), layer thickness, point elasticity, compression modulus, pressure redistribution, and what some people call âpushbackâ and the âfeelâ of different materials.
There is more about âpushbackâ in post #2 here.
Dunlop actually has a lower resilience than Talalay in most cases and lower hysteresis (the opposite of resilience and is the amount of energy a material absorbs instead of returns).
When your body is at rest it canât tell the direction of force (either from a material pushing back or your weight pressing down) because all the forces are in equilibrium. Once youâve âstoppedâ sinking in then there is only pressure along your body profile which has no direction.
Dunlop and Talalay also have a different compression modulus so if you have a layer of each material that were cut from the same ILD core then if you pressed it only a little bit the Dunlop would be a bit softer (the initial compression isnât as firm) but if you squeezed it more deeply then the Dunlop would be firmer because it gets firmer faster as you squeeze it more. ILD is only measured with the original 6" core and is the amount of force that it takes to compress it 25% of its thickness with a 50 sq in compresser foot. In some areas of the world the âstandardâ ILD is tested at 40% rather than 25% which would produce completely different numbers.
If you have a tight drum for example and you dropped a ball on it the ball would bounce quite high because the drum has a high resilience and returns most of the energy of the falling ball. On the other hand if you dropped the same ball on a spring then it may also have the same rebound (resilience) but the spring would compress more deeply than the drum surface before it launched the ball back into the air. The spring in other words would be more âspringyâ even though the resilience was the same and the drum may feel more âbouncyâ (I know these are somewhat subjective terms but Iâm using them for clarity). Talalay feels more âspringyâ because it sinks in more deeply than Dunlop before it stops so the amount of up and down movement is more and it also has a higher resilience. In other words it feels more âlivelyâ than Dunlop which is why some people say it has more pushback (it allows for more movement). the firmness or softness of both types of latex wil also affect itâs âbounceâ or âspringinessâ.
When you lie on a material and sink into it your weight is re-distributed according to how well the material conforms to the exact shape of your body (point elasticity), its softness, and how quickly it becomes firmer. Different materials and designs re-distribute weight in different ways and to different areas of the body and have a different âfeelâ which means that each material or design may have itâs own unique areas of greater or lesser pressure.
All of this together adds up to the âfeelâ of a material and mattress design and different people have different preferences and sensitivities to different designs and materials. I prefer the more lively âfeelâ of Talalay for example while my daughter prefers the less lively âfeelâ of Dunlop.
The Talalay layer you were squeezing may also have been firmer than the Dunlop because Dunlop cut from different parts of the original 6" core will have a different firmness (the bottom half of the core is firmer than the top even though they would both have the same âfirmnessâ rating because only the core itself is tested for firmness).
Polyfoam has lower resilience and higher hysteresis than either Talalay or Dunlop and in an equivalent softness rating or ILD will âallowâ the heavier parts of the body to sink in more. It is a much less supportive material than latex in the sense of having a lower compression modulus and getting firmer less quickly than latex. Itâs also not as point elastic as latex which means it doesnât conform to the shape of the body as closely.
All of these materials also have a different compression curve because only metal springs have a straight line compression. The compression curve of foam is shaped more like a banana (you can see the compression curve of some Talalay and a spring here and of some polyfoam here) and the difference between Talalay and Dunlop here. The initial resistance of some types of foam is higher until the cell walls start to bend and the rate of firmness increase slows down until finally the foam cells are mostly collapsed and the resistance rises very rapidly again. Each different version of a material can have different specs and compression curves which each re-distribute weight differently.
All of this can be very difficult to analyze or measure accurately and the subjective âfeelâ that results from the technical specs is difficult to describe but your body will âcut throughâ all the specs and tell you what it likes and doesnât and produce âsymptomsâ when a design isnât suitable for it. The hard part can be figuring out what the symptoms are pointing to and what to change with all the technical specs, possibilities, and variables involved and the somewhat subjective nature of how our bodies actually âfeelâ all the different specs.
Whatâs clear to me is that in its current configuration your mattress isnât âworkingâ. Whatâs less clear is what exactly needs to change and this can take some experimentation and trial and error to get a clearer idea and clues to the exact source of your symptoms. Even configurations that make things worse can sometimes provide clues about what will make things better.
Phoenix
