I agree on the exaggeration with the supposed compression effects of modern synthetic sleeping bags. I have one bag in particular that is only used in the cooler fall months and after being stored moderately stuffed all year,it decompresses quite well.

On the other hand, I have old synthetic winter bag, about 23 years old that is rated to -30C. Nowadays, that bag rarely gets used and does not decompress very well on its own. However 15-20 minutes in a cool clothes dryer, springs it back to its normal loftiness.
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Earth and sky, woods and fields, lakes and rivers, the mountain and the sea, are excellent schoolmasters, and teach some of us more than we can ever learn from books.

John Lubbock