Intentions for the proposal of a “calculated loft” metric

If someone is attempting to assess the general insulation of a panel of a down item, they would need to know two main things. On one hand there is measured loft, which is the physical space filled with insulation. The other is the quantity of fill in that space. Both Total fill weight and calculated loft are quantity metrics only. The idea around switching to calculated loft vs TFW is to get the quantity side of the equation into an objective and accurate statement. As we have seen, TFW is not an accurate gauge for quantity because that amount is spread over variable areas. It can only be used to compare exactly similar items and it needs to be divided by fill power to calculate total down volume. Calculated loft is an objective and accurate metric that tells you exactly how much fill is in any given area, that can compare any other down fill item to any other down filled item, with no formula or interpretation needed. It is already in volume.

However, people get hung up on comparing them with TFW as a single metric for warmth and calculated loft as a more subjective metric that requires assessing measured loft. The fact is that neither of those are independent, tell-all metrics and both require the same assessment of measured loft. Neither one of those is a whole picture of warmth. Both of them are only pictures of quantity. It’s just that calculated loft is accurate, exact, and easy. The other is inaccurate, can only be used for limited comparisons, and needs a formula to convert to volume. Regardless of which one you are using, they are only a foundation from which to assess the rest of the picture, which is measured loft.

Sure, TFW is currently used as a single metric, but that isn’t an accurate usage. The picture of “warmth” that it provides is off by absolutely massive margins. It’s basically a shot in the dark because it isn’t communicating quantity accurately and completely ignores the measured loft side of things. People have become used to assuming the TFW is a single accurate metric and when you tell them that calculated loft isn’t a single accurate metric, they jump to the incorrect conclusion that calculated loft is inferior. It’s actually far superior, it’s just that neither one of these quantity metrics are supposed to be used as a single picture of warmth. Either way, whether you want to attempt to use quantity as a single metric or not, having a one that is pinpoint accurate is much better than one with a variable margin of error that is typically huge.

The measured loft side of assessing warmth is much, much more subjective. There are a lot of elements that come together to affect the final measured loft. You can isolate many of those by just focusing on what the final physical measurement is, but even that is a little subjective. It needs to be an average of high spots and low spots across a defined area and those measurements need to be taken with a perfectly even fill distribution. It is very worth discussing how to best communicate this, because it is very, very important….but I don’t currently have all the answers here.

The real point is that you are either using total fill weight as a quantity metric with a 20% margin of error, and then having to assess measured loft on top of that. Or…..you are using calculated loft as a perfect, objective quantity metric and making measured loft assessments from there. The uneducated comparison is that TFW is a single general warmth metric and calculated loft is a confusing metric that requires a lot of subjective assessment. The reality is that both require this subjective assessment but one starts from an exact point and the other is a vague and unknown starting point. The options look like this….

With TFW, the builder needs to specifically tally this up for the consumer, as it isn’t part of building. Then, the consumer can only compare a jacket with a collar to a jacket with a collar. They cannot compare a collared garment to a hooded garment. Then, if one garment has 800fp and the other has 900fp, then they need to multiply the total weight by that number to get total volume. Then, they will have two numbers to compare, but because that total is spread over an unknown area, there is a margin of error that can be 20%. Then, they need to assess the measured loft contribution from there.

With calculated loft, the builder already has the number. They typically would use it to fill every chamber and can easily just hand it over. Then, the consumer can use that very number to compare the fill quantity of any down item, whether it is a collared jacket to a hooded jacket or a hooded jacket to a quilt…..or a quilt to a mummy bag. They also don’t need to do any math at all, since it is already in volume. A 2″ calculated loft in a jacket is the exact same fill amount as 2″ calculated loft in a sleeping bag and there is no margin of error and no interpretation. Then, they need to assess the contribution of measured loft from this point.

There is no perfect, single metric that tells you everything, and it isn’t likely to exist. Until then having a perfect quantity and a general idea of measured loft is enough to get someone with a basic education, really, really close to an accurate picture of warmth.