Connecting a boiler outdoor sensor

What type of cable should I use to connect an outdoor weather sensor for a condensing combi boiler?
The manual specifies 2x0.75mm cable as a recommended minimum.
I found the following cable - http://www.tlc-direct.co.uk/perl/search.pl?search=0.75&button=Search - though i'm confused as to what sheathing material is suitable for outdoor use.
Any advice greatly appreciated.
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