Hi ds_express,
This probably means that the G30 was 30 IFD and the G50 was 50 IFD (IFD means Indentation Force Deflection which is a measurement of foam softness and firmness similar to ILD or Indentation Load Deflection which is more commonly used with latex). It is determined by how much force is required using a 50 sq in round deflector foot to compress a 20" by 20" 4" thick foam layer by 25% of its thickness or 1". IFD can also be measured at other percentage thicknesses. 5o IFD would be significantly firmer than 30 IFD.
There is no way to answer this on an individual basis outside of your own personal testing. Although it is a commonly used word … support in a mattress is really not that meaningful a term because it is so vague and has multiple meanings. One of the two main functions of a mattress is to keep your spine and joints in neutral alignment in all your sleeping positions. If a mattress keeps you in good alignment in all your sleeping positions and “stops” the heavier parts of your body from sinking in too far relative to the others and “allows” the lighter parts of your body to sink in enough relative to the other parts of your body then it would have adequate support regardless of its firmness level. If it “stops” the lighter parts from sinking in far enough or “allows” the heavier parts to sink in too far … then you would not have good alignment and the “support” under the part of your body that was sinking in too far or not enough would either be too much or not enough for you. Neutral alignment is the goal and the level of support under each part of the body is only the means used to get there.
“Primary support” generally comes from the deeper parts of the mattress and is primarily responsible for “stopping” the heavier parts of the body (the pelvis). Secondary support generally comes from the upper parts of the mattress and is the part that “fills in the gaps” in the sleeping profile and helps to maintain the natural inward curves of the spine. The upper layers also need to allow the “bony prominences” of the body such as the hips and shoulders to sink in enough to redistribute and relieve pressure. in other words … a mattress is always a combination of surface softness which “allows” parts of you to sink in enough for good pressure relief and good alignment and deeper firmness which “stops” the heavier parts from sinking in too far.
Every type of foam gets firmer as it compresses more at different rates so for many people a 6" layer … depending on what was under it and on the type of quilting and ticking used for the mattress … could provide good pressure relief and alignment. In other words it could be both soft enough with its initial compression to relieve pressure and firm enough as it compresses further to keep a specific person in good alignment. Other people may need a firmer support layer with a softer comfort layer to provide the combination of pressure relief and alignment that was best for them. They may need a softer upper layer that “allowed” more and a firmer deeper layer that “stopped” sooner.
Again … the only way to know for certain is with your own personal testing on the specific combination of foam and other components (foundation, innerspring, quilting, ticking) that you are considering. If the 6" layer provides you with good PPP (Pressure relief, Posture and alignment, and Personal preferences) … then it would be supportive enough for you. For other people, a 6" design … particularly on a firm non flexing foundation … may not provide enough thickness to provide the combination of pressure relief and support they need in a single layer. Higher weights tend to do better with thicker mattresses which compress more gradually and are more adaptive and thinner mattresses tend to be fine for those that are lighter but there are no rules here. You can read more about some of the potential benefits of a thicker mattress in post #14 here.
There is no “theory” that can predict or “translate” one design (apples) into another (oranges) except by educated intuition or guesswork and based on averages for your body type and sleeping style. This is the reason for a longer conversation between you and a manufacturer you are considering who is in the best position to provide this kind of guidance. They know the details of their own mattresses and how all the different layers and components interact with each other and different types of people better than anyone else. These types of comparisons are only really relevant with mattresses that have a very similar design and other than that would require some guesswork based on their experience with their own mattresses.
I don’t recommend firmness or comfort levels. I only speak to the quality and value of mattresses and I leave the comfort choices to your own personal testing and more detailed discussions between you and the manufacturers or retailers. My goal and the goal of the site is to help you eliminate all the worst choices and then help with “how” to choose … never “what” to choose. The people who actually sell mattresses are always the ones that can provide the most meaningful guidance or comfort choices.
The better options and possibilities I’m aware of in the South Florida area (Miami, Ft Lauderdale, West palm Bech) are listed in post #2 here.
Phoenix