The heat pad should be placed in a dedicated internal pocket or sleeve, not loosely inside the stuffing. This pocket should be:

1. Snug but Not Tight: The pocket's internal dimensions should be approximately 0.5 to 1.5 cm. larger than the heat pad in both length and width.

• Why? This allows for easy insertion and removal without forcing it. A pocket that is too tight can strain the seams; one that is too loose allows the pad to shift and potentially create uncomfortable hot spots.

2. Account for Expansion: Some heat pads (especially grain/seed-based ones) expand slightly when heated. The extra space mentioned above usually accommodates this.
3. Crucial Air Gap Around the Pad: This is the most important factor. The pocket must be positioned so that there is a buffer layer of stuffing (at least 2-3 cm) between the pocket and the outer fabric of the toy.

• Why? This insulation prevents the heat pad from becoming dangerously hot to the touch on the toy's surface, ensuring it delivers gentle, diffused warmth rather than a direct, concentrated heat that could cause burns.

4. Consider the Pad's Thickness: The toy must be thick or plump enough so that when the pad is inside its pocket, the toy does not become overly rigid or lumpy. The overall toy should still be soft and huggable.

Example:
If your microwavable heat pad measures 15 cm x 10 cm , you should:
Create an internal pocket of about 16 cm x 11 cm .
Ensure this pocket is sewn into the center of the toy, surrounded on all sides by at least 2-3 cm of polyester fiberfill or other safe stuffing.
The finished toy's dimensions must be large enough to contain this "sandwich" (outer fabric + stuffing + pocket + stuffing + outer fabric) comfortably.

In summary: Think "insulated pocket." Reserve space slightly larger than the pad itself, but the most critical design element is ensuring sufficient insulating material between the heat source and the user. Always include clear instructions with the toy to never microwave the toy itself and to always test the heat pad's temperature on the inside of the wrist before placing it inside the toy.