Save on Shipping and Other Details
It's the size of the box not the amount of filament that determines the price of most small package shipments. Knowing how much 3D Filament fills a package or, just as importantly, at which point one more spool requires a bigger box goes a long way to reducing how much is spend on shipping.
The following breaks down the proportionate number of 1kg and 200g spools that fit in each shipping service if you want to leverage this in your favor (I recommend it). For example, up to '9' 200g Spools will fit into a USPS Legal Flat Rate Envelope, 1kg Spool and '5' 200g Spools, or '2' 1kg Spools by themselves.
$4.21 First Class fits (1kg, 200g) - (0,1)
$5.75 USPS Flat Rate Envelope fits (1kg, 200g) - (0,6), (1,0)
$6.05 USPS Legal Flate Rate Envelope fits (1kg, 200g) - (0,9), (1,5), (2,0)
$9.74 USPS 0.2 Cubic ft. fits (1kg, 200g) - (0,12), (1,8), (2,4), (3,0)
$12.18 USPS 0.3 Cubic ft. fits (1kg, 200g) - (0,17), (1,12), (2,7), (3,1)
$15.40 USPS 0.4 Cubic ft. - TBD, Still hunting down the box.
$18.50 USPS 0.5 Cubic ft. fits (1kg, 200g) - (0,26), (1,22), (2,18), (3,14), (4,10), (5,2)
$23.00 FedEx Ground fits anything greater than the 0.5 Cubic ft. is the flat fee and I'll cover the difference as the weight increases.
We'll be dialing this in as the spool changes and better boxes are found. Your filament needs to get to you safely and work well down to the very end. The current tight center core and relatively small 6" flange is more or less specifically to take advantage of that sweet, sweet Legal Flat Rate Envelope. If the consensus is that the spool dimensions need to change for ease of use, I'll rework the packing and boxes to suit.
What about free shipping, everyone loves free shipping? I've offered free shipping, the problem is you have to build in the distributed shipping costs across your products. What ends up happening is lots of half filled boxes with full price shipping paid for by everyone else. It also discourages sales or low price items because you're terrified everyone will unknowingly structure their order such that the shipping costs LOSE you money on the sale. Which is terrifying because it's happened. I'd much rather optimize the format for efficient shipping so I can lower the cost and pull back the curtain on my shipping economics that allow you to get the best bang for your collective buck.