A microwave is necessary to heat up flaxseed pillows.
Not all microwaves are created equally. Some are more powerful than others, and this has to be taken into account when heating a flaxseed pillow the first few times.
Recently we moved to a new apartment with a new-to-us microwave, which meant we had to figure out the right amount of time to heat our flaxseed pillows. To do this we heated a flaxseed pillow for a minute at a time until the pillow was the right temperature. Now we know how many minutes to heat our pillows, and plug that number directly into the microwave.
Flaxseed pillows can be very hot, so always be careful with them, especially around children and those who are sensitive to heat.