I have a 10 year old Kelty Cosmic 20 that's probably been slept in for 30 odd nights over the years. Lately I've been using it with a Nemo Tensor insulated pad and a Sea to Summit liner that supposedly adds 14 F to the rating, but I've been cold at temperatures in the low to mid 20s, even while wearing a puffy jacket and a hat.

Does down degrade permanently over time? Is it time to buy a new bag, or will I likely have a similar issue with a new 20 F bag? Is it potentially an issue of it needing a wash? It's not visibly dirty but I don't know how long it's been since it was last washed, and there may be some body oil or similar impacting the warmth.

Thanks for any insight!