Two tops is not necessarily warmer than one top. Though once you get to three layers you're naturally restricting air movement quite considerably. ie, a sub shirt, armour, bike top. As you know by now, quite a few single layer armours are stupidly hot due to poor design.
Take a TLD7855 for instance. You really need to wear a top under it as it nipple rubs and glues itself to you, so you can't get it off - well, assuming you get sweaty from riding hard. As the tld7855 breaths so well and the armour is light, not like the heavy super hot reactive foam types, that combination is generally fine for most conditions - unless it's say 35c - then I find it starts to get too warm.
If I also decide I want more protection and wear a 5955 over a 7855, which both on their own are cool (ish) - together I find they get too warm in the summer.
It's just finding your way through the balance between what type/coverage of protection you want, combined with what weight/bulk you find acceptable, combined with if you do or don't want/need to also wear a shirt over the top, mixed in with what temperatures you ride in and what heat levels you find acceptable.
A leatt armoured T is very breathable. Just on it's own it makes a really good hot weather top if you don't mind riding in a compression top and at least you have some shoulder protection. A 5900 or 5955 over the top of that doesn't make things much warmer, it's slim so you don't know or feel you have it on and you get excellent chest/back protection (if you ignore the short back - but I'm presently riding with a bum bag so that's fine). If you want elbows, you then also need something like a leatt 6.0. So price wise that setup becomes a bit stupid, but does give great flexibility for different rides and adding or removing bits as required. Have a fox baseframe on order to also try with the tld5900/tld5955 as this has shoulder and elbow protection all in a mesh base layer.
Arguably,
@Hamina's Leatt 6.5 is far better value and a good bit cheaper than a leatt T, tld5955 & Leatt 6.0 elbows. The base layer looks great, but you can't buy more to have spares/when you tear it or to put one in the wash. The outer armour is substantial and no doubt very effective, but for me looks a bit bulky and hot - especially compared to a tld5900 which you could wear under a shirt and not really know you have it on. It will be interesting to see how he gets on with it long term as it does look like a great bit of kit.
www.freewheel.co.uk
. Breaths well with the bumpy and vented skin side pad and great for carrying the basics. Normally stick the full 1.5 litres in it and think nothing of it. When you hook the tube up (magnet and clip) make sure you have the pipe all fed through (so it sits flush with your waist) or you can catch it on the saddle with on and off's. I feed the pipe through the hole and then through the back of the right hand belt pocket so it doesn't sag.
