360° View - Glacialtech Igloo 5751 PWM Heatsink Information on Frostytech's test methodology is available here.
There are two 25x92x92mm fans on the Glacialtech Igloo 5751 PWM heatsink. The top spins at 1400RPM, the bottom 800-1800RPM depending on demand. Power is supplied to both fans via a single 4-pin PWM motherboard fan header. The seven bladed impeller is not protected by a fan grill, so watch out for loose wires. With the upper fan removed we can see the four 6mm diameter heatpipes threading though the 40 or so 0.3mm thick aluminum fins. The aluminum fins are spaced ~1.5mm apart.
Standing 126mm tall, the Igloo 5751 PWM heatsink conveniently uses tool-free Intel clips and fairly easy to install AMD brackets. The Intel clips quickly lock into the PCB holes surrounding the LGA775 Intel processor socket, the AMD bracket requires a screwdriver. Notice the small 19mm tall extruded aluminum heatsink which forms the base cap for this heatsink. The heatpipes are soldered to this component, and the form fitting 2-5mm thick copper base pad below.
The Igloo 5751 PWM's two fans exhaust directly towards the base of the heatsink. The four heatpipes are soldered to the base, but not to the aluminum fins. The copper base measures 33x33mm in size, which is a little undersized for AMD processors which have a 37.5mm square integrated heat spreader.

Base Finish and Flatness

Flipping a heatsink over to inspect the business end is often a simple indicator of overall cooler quality. More practically speaking, a heatsink is in many ways only as effective as the contact it makes with the processor - the flatter and smoother the better. Base finish is one of the criteria that Frostytech measure in the course of evaluating heatsinks, and it involves two distinct aspects. Surface Finish is the first; this is calculated with the aid of Surface Roughness Comparator that has a cross section of common machine surface finishes and their numerical surface roughness equivalents in microinches. The second is Surface Flatness. This is tested with an engineers straight edge or proven flat surface, in two axis.

The base of the Glacialtech Igloo 5751 PWM heatsink has a surface roughness of ~16 microinches, which is considered excellent. The nickel-plated copper base itself has finely sanded finish that is perfectly flat in one axis and slightly convex in the opposite.

Sound level measurements are coming right up next.