Thermalright SI-128: Evolution of a Past Master

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The SI-128 is the sequel to the SI-120, which in turn evolved from the XP-120: One of the first heatsinks to use a 120mm fan and a longtime SPCR favorite. The basic idea is the same: A bed of fins suspended horizontally over the CPU socket, with the fan blowing down. What's different? The SI-128 increases the depth of the fins and widens the "wingspan", with a corresponding increase in surface area and — hopefully — cooling power.

We say "hopefully" because the increase in surface area has also increased the airflow impedance. The gap between the fins is much tighter than the previous models, which means a faster fan is probably needed to utilize the full cooling potential of the SI-128.

It's big and blocky: You can barely see the base under the fins.

The SI-128 is fairly tall for a "top-down" heatsink, especially when the space required by a fan and its airflow needs are added in. At a little over 90mm tall, it probably needs about 130mm above the surface of the CPU to be effective.

Two support struts give the SI-128 a very sturdy look and feel.

The SI-128 gets by with surprisingly few heatpipes: Four. But, they're four extra large ones, with a hefty 8mm diameter. Do larger heatpipes carry more heat? Only Thermalright knows for sure, but it seems likely enough; the cross-sectional area of an 8mm heatpipe is almost double that of the more common 6mm variety, which means the internal volume is probably about twice as much for heatpipes of similar length.

A glamor shot to make the heatpipes look bigger.

In spite of its exceptionally shiny appearance, the SI-128 is not made of any exotic materials. It's an aluminum-copper hybrid, just like almost every other heatsink out there. So, whence comes the shiny metallic appearance? The copper base and heatpipes are nickel-plated, smoothing out the appearance and leaving a higher-end, more finished look.

Fin spacing is quite dense, which makes us worry about low airflow performance.

The base has the painted, lustrous smoothness of a nickel-plated surface — or at least it appears to. On closer inspection, there are actually hundreds of tiny ridges that can be felt with a fingernail, but seen only with great difficulty.

The base looks smooth as a mirror, but it's faintly textured with tiny ridges.

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