I've been looking around for some winter boots, and was confused by all the ratings for warmth that were based on "grams of Thinsulate" insulation. Not having had boots rated like this, seeing the numbers vary from 100 to 1200 grams meant little to me.
After some digging, I didn't find the answer in any blog posts, hunting reviews, or footwear guides. Instead, I found it in the unlikeliest of likely places, on 3M's website (the manufacturer of Thinsulate insulation).
Here is the information from the site, in case it ever disappears.
3M™ Thinsulate™ Insulation for Footwear
3M™ Thinsulate™ Insulation – a Premium insulation choice for footwear
Thinsulate insulation works in footwear‚ including winter boots‚ hiking boots‚ hunting boots‚ or casual shoes‚ because it doesn't bog boots down with weight and the fibers absorb less than 1 percent of their weight in water. This means it’s not only one of the lightest synthetic insulations on the market‚ but it helps keep feet warm even in damp conditions. So‚ look for Thinsulate insulation in warm boots or shoes that need to hold up to cool or cold temperatures and damp conditions. It also comes in different gram weights to provide the right warmth for your activity‚ so use the guidelines below to select the appropriate footwear.
Recommended grams of 3M™ Thinsulate™ Insulation for footwear:
- 200 grams* for cool conditions or high activity levels – Recommended for work boots‚ hiking boots‚ rubber bottom boots‚ hunting boots‚ snowboard boots‚ alpine ski boots‚ or athletic winter boots.
- 400 grams* for cold conditions or moderate activity levels – Recommended for rubber bottom boots‚ hiking boots‚ PAC boots‚ hunting boots‚ or work boots.
- 600 grams* for very cold conditions – Recommended for hiking boots‚ work boots‚ hunting boots‚ or PAC boots.
- 800 grams* for extremely cold conditions with light activity levels – Recommended for hunting boots‚ PAC boots‚ or work boots.
- 1‚000+ grams* for extremely cold conditions with light to minimal activity level – Recommended for unique applications requiring additional insulation.
* Grams per square meter of insulation
Keep in mind that these ratings are meant to be true when the footwear is worn with a liner sock, and a heavy winter sock, not just a cotton athletic sock. Also take note that everyone's perception of cold will vary.