advice about making lavender & wheat/heat packs

[Rosendula]

I've decided to make some lavender and wheat heat packs that can be heated in the microwave. Can someone please answer these questions/give some reassurances. I want to make heat packs, not do some kind of Brainiac Science Abuse-type microwave experiment.

1) Is there any type of fabric I should avoid? I managed to get hold of some cloth napkins from a charity shop that are the ideal size, but I don't know what they're made of. They feel cottony, but tbh I don't have a clue

2) I was thinking of drying my own lavender to use. Is that OK? Or are these things usually just 'lavender fragranced'? I don't need to 'treat' it in anyway to stop it being flammable do I?

3) The wheat I have to hand is my chicken food. Again, should it be 'treated' first? And does it matter if a bit of corn (maize) gets in there?

4) Assuming your previous answers don't put me off making them, how do I work out how long to heat the pack for without setting fire to it or exploding the microwave?

Thanks for any advice. Total noob with this sort of stuff.

(Oh, and just for interest, the napkin 'rings' that came with them had a lovely bow on them which I'm going to turn into hair bobbles for my little girl. So from each napkin I should get 2 heat packs and a bobble - for 25p plus chicken feed )

[Green Aura]

Only use natural fibres, synthetic fabrics could catch fire.

Home dried lavender is fine, no it won't catch fire.

Your chicken feed should be fine, or you can use rice.

Only fill the bags half full of a 5:1 grain:lavender mix (or hops for sleeping).

Heat on full for about 30 second blasts then 10 seconds more etc until hot enough. I've had a client who burned her back using one.

[Rosendula]

Thanks Maggie. That's really helpful. :)