The maker of Wiggy's sleeping bags claims his bags suffer no loss of loft/warmth from compression, and even offers a vacuum packed option, or used to, anyway.

"The Lamilite is an unbounded, silicone-coated continuous filament fiber. This is inside and cannot be seen. The silicone coating gives the fiber two very desirable properties. The first is “antistatic” which allows the fibers to perpetually repel each other regardless of how tightly the fibers are packed against each other (such as compacting in a stuff sack). The loft always returns after removing our sleeping bag from the stuff sack. As an example, one of our Ultima Thule sleeping bags was compacted under 20 tons of pressure. It was blister packed in two poly bags the size of 14 1/2” x 9 1/2” x 2 3/4”. After four days it was opened and in one hour, without assistance, 90% of its loft returned. A Lamilite insulated sleeping bag is the only synthetic bag ever put through this test that returned to its original loft. Not even a down bag will return to almost original, actually the down bags deteriorate when vacuum packed. It is for this reason that I guarantee my sleeping bags will never lose their loft. The Alaska National Guard, as part of their survival gear, uses the Ultima Thule. The bags are left in the vacuum package until needed."

Usual disclaimers, never owned one, no connection, etc.