Silica

[hurly]

Sometimes when you buy a product, there's usually a little white bag (closed) with SILICA (GEL). What exactly is it and what does it do?

It says "Throw away, do not eat"

I found the bag inside my exercise (iron pumping) kit...

[James]

It absorbs water.

[Dr.Stein]

Yes, it is an absorbent. It acts to absorb water to prevent moist environment. Moisture will simply destroy things.

[chemistry_freako]

yeap - silica gel's a dessicant (meaning it absorbs water vapour from the air so as to prevent/ minimise food spoilage) as it absorbs water readily due to it's high porosity.
They also often come with an 'indicator' (e.g. anhydrous cobalt II chloride) which has a different colour when anhydrous, and when hydrated