Depends what you mean by help, any sort of PC, Armour carrier, vest or large chest rig will inherently hold in heat. It's just a couple of layers of thick, non-breathable fabric - physics.
Technically speaking when you don't need to protect your vital organs from bullets and frag a belt rig and layering with some jackets is better overall because you control how you layer up or down (and adjust heat retention with zips), whereas a piece of load-bearing equipment on your torso just retains a fixed amount of heat and sweat with no capacity for adjustment.
Which layers to wear on your torso all depends on activity levels, ambient temp and precipitation/wind, plus it's also kind of a personal thing depending on how hot you personally 'run'. If you're always red and sweaty and rarely stand still then probably just a wicking t-shirt with uniform shirt/softshell jacket. If you're cold blooded and lay on the ground a lot then a long-sleeve insulated base layer followed by mid-layer (PCU L3 thick fleece, PCS issue 'buffalo' etc) with a smock or softshell over the top might be good. That would be a super simple breakdown of the bare bones for a typical UK autumn/winter day.