ok, there are retailers who try to cut corners to save $$. eg. they offer you system 3 at (est) $3.4k, generally the air-con mfgr specs will specify wat type of material to use, eg. for insulation, piping, etc. so they cut corners by finding something that qualify for the specs technically but the material could be inferior made or from china. no offence and biased against china products but some are like backyard plant where these products are of low quality, eg. no QC, R&D etc. these will be called alternative offer products in constrn line. so frm there, they can save coz they order in big bulk. eg. bulk order of armflex vs 'alternative products', juz imagine hw much they able to save! basically, for (eg.) $3.4k system 3, you are paying for armflex, and not any other alternative products, why would you settle for less? from my understdg, for this price, it can offer armflex, kflex etc already. whether its condo or HDB, residential air-con basically all the same. SO DO NOT SETTLE FOR LESS, unless they give you 2sets of system 3 at $3.4k the above is commercial reason. technical reason is that if you should use alternative inferior quality products, next time if got leakage, condensation, product deteriorte and require changing, den you will hv a big headache. a vy simple way to differentiate is to touch and feel both the products. i don't know the grey type is it the type i seen b4, coz i ever seen the grey type of insulation which feels like foam. cannot make it to my requirement and std. and also dun be bluff by retailers. air-con trunkings can be hidden in hdb units as well if one do hv cabinet, false ceiling etc. condo is becoz ppl pay $ for nice nice architect design which must incorporate the ultimate ***** different from other condos. usually theirs are not really concealed also. juz imagine if fully concealed, den if got leakage, hw? hack the whole false ceiling? the owner will sue the management until they die man... coz spend so much $ to buy hazzle condo meh? its juz dat in condo, the architect & m&e consultant had design the air-con routing nice nice already. if for those vy ex condo, their air-con are bigger size type, eg. VRV system (these are known as ducted unit) where ducting is used. different from split units.