At a boot sale I saw some proper army surplus (MOD) camelbak pouches (made by Camelbak) on sale. But looking at them I wonder if it is possible to remove the bladder and replace it? At first sight it doesn’t look like it’s possible to unscrew and remove the cap.

Yes you can. It takes a standard three litre bladder.

The weakness are the shoulder straps as they are not padded as the Camelbak is designed to clip onto other equipment.

Thanks! That’s useful info to know. Though I thought that civvie biker camelbaks were 2 litre…

So how would I go about removing the bladder?

Though I thought that civvie biker camelbaks were 2 litre…

They come in a few different sizes.

Indeed. And I’m old enough to remember the very first ones…