answered it in the other coppins duplicate post but moved it to here in case you missed it first time
Water, If they are the denser premium coppens they will withstand quite a bit of soaking in water, I am guessing you want to feed them for fishing up in the water? if so take some 4 mm pellets soak them for about 5 minutes the night before, strain them but leave them quite wet and bag them, the following morning they will be a bit bigger 5-6 mm. ideal for fishing a 6 mm hard on the pellet or even banding one of the soaked pellets.
They will definitely sink slower.
If using the very light coppins which break down quick then just do them on the day as soon as you get to your peg, 4 mm soak about 3 minutes and drain with a sieve, they will expand and be lighter about 45 minutes later.
also if you leave them in shallower trays after soaking in the sun they will remain expanded but the water will dry out from them making them in lighter