A thought occurred to me about the idea of combining Apex with down and Apex with Primaloft Gold insulation.
Electrical static charge may affect how these interact. I know that lower surface energy, more hydrophobic plastics and human made rubbers like polyester/PET, PU, PE, PP, silicone, etc tend to attract electrons to their surface when in contact with other materials (especially being rubbed/moved back and forth) and thus build up a negative charge.
Meanwhile, more natural, hydrophilic materials like hair, silk, leather, wool, the non hydrophilic and semi natural exception–glass, and the harder to classify dry human skin, when in contact with other materials (especially when rubbed/moved back and forth) tend to build up a positive charge from loss of electrons.
Opposite charges attract. It’s how a duster works, the duster becomes negatively charged and attracts the positively charged dust. Or when you rub a rubber balloon on your head and your hair and the balloon attract each other.
This can have implications for different combos of material within the same fabric sleeve. A non treated down, most likely would become fairly positively charged while a silicone treated polyester (Apex) would become fairly negatively charged. If so, besides the friction factor mentioned earlier, the opposite charges of the materials will tend to attract them to each other, potentially also helping the down to stay more in place.
Conversely, Apex and Primaloft Gold would both develop a fairly negative charge and thus tend to repel each other, making it work less better as a combo?
Obviously this would apply most during cold and dry weather, and less so during humid weather. I’m quite curious about this now. Particularly about whether or not untreated down will tend to “static cling” to Apex and vice versa. Combining them in one piece could save weight and sewing time/complexity, when it comes to cold weather camping where you want the down on the bottom and a synthetic above to deal more with moisture via condensation. Basically cutting out the middle man of putting an extra synthetic quilt on top of a down quilt or bag–you would save weight in fabrics both from not using liner/face fabrics, but also no extra baffle material and thread.
(I primarily hike/backpack in cool to cold conditions, sometimes in somewhat more extreme cold like single digits and negative single digits F., hence I have a high degree of interest in such systems to deal with moisture more effectively).