Nomex is an aramid fibre - the same family of material used in fire-resistant clothing and heat barriers - which is why it appears in hose construction where heat and strength are both required. In a silicone hose it is built into the wall as a reinforcement layer, woven or wrapped between the layers of silicone rather than applied to the outside.
This is worth being precise about, because it is often misattributed. The burst strength of a reinforced silicone hose comes from the reinforcement layers built into its wall. Nomex is one of the materials used for that reinforcement, and it brings its own heat resistance to the job, but the pressure-holding capability is a property of the reinforcement structure as a whole - not of the Nomex fibre on its own. A hose that is described as reinforced is relying on that layer to stop it splitting under boost.
A hose under boost does not usually fail by bursting immediately. It fails by swelling. An unreinforced silicone hose will balloon outward under pressure, and that changes more than the hose's appearance. It increases the internal volume of the intake path, it can pull the hose partially off its pipe at the clamp, and it changes the effective diameter of the path the air is travelling through. On a charged engine, the intake system is calibrated around a known geometry. A hose that changes shape under load changes that geometry.
The practical job of the reinforcement layer is to keep the hose from ballooning so that it holds its shape and its internal diameter under pressure. That is why reinforced construction matters most on charged applications - anywhere the hose is being pressurised rather than just carrying air. On a naturally aspirated intake path, the hose is not fighting pressure and the requirement is different. On a boosted one, it is.
Reinforcement sits inside a silicone wall that is already doing thermal work, so the reinforcement has to survive the same temperatures as the hose itself. A reinforcement that degrades at temperature stops reinforcing, even if it looks intact from the outside. Nomex is chosen for these constructions precisely because it holds up under heat.
Reinforcement is inside the wall, so you cannot see it from the outside. What you can do is ask what the hose is specified for. If your application runs boost, ask whether the hose is reinforced and what the construction is. You can see our reinforced range on the Nomex reinforced silicone hoses page, or send us your application and boost level and we will specify it.
