Cond. reducing runes stack add/multi?

Title says it all basically, do the runes, gear and skills which reduce the duration of condition stack additively or are they multiplicative?

For example if Im using Featherfoot Grace with a -20% cripple rune and a -20% cripple shield and get hit with a 10 sec cripple how long will it last?
3 or 1 secs?
Thanks

I don't know personally, but you can test it on the Isle of the Nameless. The Master of Conditions on the beach should be able to help.

I think they stack additively, so it will be 10-10*0,4=6 seconds.

EDIT: Tested at Isle Of The Nameless using a timer:
Estudent of Crippled = 10 seconds crippled
With Restoration Rune = 8 seconds crippled
With Restoration Rune + -20% cripple Shield = 6 seconds.

So they stack additively.