Posted on

Sea to Summit down sleeping bags, part 4: EN temperature ratings

This spring season, Sea to Summit has released a groundbreaking new line of down-filled sleeping bags. The Sea to Summit down sleeping bags are so packed with technology, it’s more than we can adequately describe on, so we’ll be examining one technological aspect each day all week. Curious how Sea to Summit’s designers have pushed the envelope with their new down sleeping bag designs? Read on. Today, we are looking at how the temperature ratings of each bag are based on actual EN-standard testing.


Another way that Sea to Summit cuts through the usual marketing hype is to have all of their sleeping bags rated according to the European standard EN13537. This EN temperature rating is performed by a third-party, and involves rigorous testing with a mannequin and various sensors in a controlled environment. The test results are split into three ratings:

  • “Comfort,” which is the temperature at which a typical woman can expect to sleep comfortably in a relaxed position. For women or cold sleepers, this is the rating you should use to decide the coldest temperature the sleeping bag is suitable for.
  • “Lower Limit,” which is the temperature at which a typical man can expect to sleep for eight hours in a curled position without waking. For men or warm sleepers, this is the rating you should use to decide the coldest temperature the sleeping bag is suitable for.
  • “Extreme,” a survival-only rating not intended for general use. This is the lowest temperature at which you can expect the sleeping bag to keep you alive in the event of an emergency.

Having sleeping bags tested in this way provides a baseline for comparing sleeping bags with one another, especially between different companies. While some sleeping bag ratings can seem optimistic (certainly we’ve all tried sleeping bags that felt cold even above their claimed temperature ratings), the EN standard helps you purchase the bag that will work best for you.

Many times, even the manufacturers who have their bags EN-rated still round off these numbers when claiming a temperature rating, and it can be unclear whether this rating refers to the “comfort” figure or the “lower limit” figure. While it might seem a bit odd that the Sea to Summit down sleeping bags feature ratings like 12° or 19° instead of nice, round numbers, but Sea to Summit has chosen to base those numbers on the EN-rated lower limit instead of what looks best in an advertisement.

That realism is something you’ll appreciate the first time you weather a winter storm in one of these sleeping bags, with confidence that your bag will keep you warm down to the specified level!


On Monday we wrote about the 3D NanoShell; Tuesday, we discussed the 3D Sidewall and Reverse differential cut. With yesterday’s article on down certification and today’s explanation of the EN ratings, we’re almost done! Tomorrow, we will wrap things up with a closer look at the individual features of each series being offered.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.