In reply to Tigger:
> The holder fabic it's may not need to be stretchy, only the bungee cord at each of the 4 corners.
The blurb in the link mentions “flexible material”. I agree it’s probably not essential but it might give a neater finish if it is slightly stretchy.
> Also by the time you've bought the necessary materials and paid for p&p, buying one pre made (£7 - £10) may actually work out cheaper.
The one linked has a nice design which would work well with my pack (that’s why I want to make something similar) but unfortunately it’s only currently available directly from Mammut at £10 plus £7 p&p. Although to be honest it’s not all about the cost - I like making stuff. Thanks though.