The first step in flower designing is to always process your flowers correctly (making sure they are hydrated immediately upon arrival. The next step is to soak your florist foam in water that has had professional florist food added.
Food and water is as essential to long life in flowers as it is to you - so treat them well! Sugary soda can cause bacteria growth - so I stick to the professional solutions by Floralife. We trusted this brand in all the shops I worked in and I sell the same to my own customers (in smaller quantities, of course!)
There may be some other floral foam that is cheaper - but I have the same attitude towards my florist foam. OASIS is a clear winner for mimicking the cell structure of flowers - it's actually been proven to extend the the life longer that flowers stored in plain water!
I takes just a short time to let foam saturate properly. Trying to hurry it by forcing it under water can cause dry pockets that could spell death to a flower stem.
Allow the foam to sink gradually, soaking up as much water as possible.
It generally takes only a couple of minutes for each brick to become fully saturated.
The water soaked brick is very heavy. If you were to cut it open after allowing it to "float soak" - there should be total saturation with no dry pockets.