Most heated sock development effort goes into the element. In practice the element is the reliable part. The pouch, the seam it is stitched onto and the point where the lead leaves the knit are where a pair either survives a winter or comes back as a complaint.
The pocket is a load-bearing part
A battery pack has mass, and on a sock that mass hangs from a knit surface that stretches every time the garment is pulled on. A pocket stitched flat onto the cuff with a single row of stitches will pull at its corners within a few weeks. The workable pattern uses a panel of low-stretch technical fabric, flatlock stitched on all four sides, with the pocket sized to the pack rather than to a nominal dimension.
Why the pocket sits below the rib
The rib is the part of the sock that has to recover its shape after every wear. Stitch a pocket across it and the rib stops recovering, the cuff sags, and the sock starts sliding down inside a boot. Moving the pocket down to the flat-knit calf section keeps the rib intact and puts the weight against a surface that does not need to stretch. It also keeps the pack clear of the boot cuff on taller footwear.
One pouch or two
A single pouch on one calf is lighter and cheaper, but it puts asymmetric weight on one leg over a long shift. Two pouches, one per sock, distribute the load and let each sock carry its own circuit, which also simplifies the wiring: no cable crosses the body. The cost is a second pack and a second charging routine, which is a conversation to have with the buyer rather than a decision to make silently.
Lead routing: the shortest path is rarely the best
The obvious route for the lead is straight down the back of the calf to the heel, because that is the shortest distance to the element. It is also the route that crosses the highest-flex region of the sock. A better pattern runs the lead down the side of the calf, parallel to the rib direction, and enters the sole channel from the outer edge. The lead then bends in one plane only, and the bend radius stays inside what the conductor is rated for.
Wash safety lives at the connector
Buyers ask whether the sock is machine washable, and the honest answer depends on a part most listings never mention: the connector where the lead meets the sock. If that joint is a soldered splice inside the knit, washing will eventually fatigue it. If it is a moulded, rated connector that the user detaches before washing, the wash cycle is a non-event. The care label has to make the removal order explicit, and the connector should be described as a wearing part with a stated cycle count.
Sizing: the pouch has to move with the foot
Pouch height is set from the floor, not from the top of the sock. Scale it by shaft length and a size XL will put the pack against the boot cuff while a size S leaves it floating above the ankle. Position the pouch by a fixed distance from the heel instead, and the whole size run keeps the pack in the same relationship to the boot.
What to document per pair
Four figures do most of the work in a buyer conversation: the heated area as a proportion of the sole footprint rather than a phrase, runtime stated separately at low, medium and high with the ambient temperature declared, the maximum wash cycles the connector is rated for, and the warm-up time measured on a sample. Anything not measured should be written as not measured.
What to write into the tech pack
Fix the pouch panel and stitch type, its position measured from the heel, the lead route and the plane it bends in, the connector type and its rated cycles, the removal order printed on the care label, and the four figures above. Then state which of those were tested on the finished pair and which are still estimates.