Cauliflower question

Mine have tight white heads about the size of a tennis ball and ive heard that you should tie the leaves up to cover the head which ive done. Does anyone else do this and why.

thanks Chappers

Or simply snap one over across it.

Stops the sun scorching them. Keep a careful eye on them, if you can see the curds already, they won't grow a lot more & can soon open up.

Or simply snap one over across it.

Stops the sun scorching them. Keep a careful eye on them, if you can see the curds already, they won't grow a lot more & can soon open up.

Spot on, I've had a couple of Cauli's earlier that were shop size and sort of just appeared under my netting amongst all the other brassica's. I pulled them and they were great.
Now they're thinned out, I noticed tonight, two small Cauli's (I planted later) that have already bolted. Do they stay covered up in some way until they are mature or think they're mature ?