Our FEEL Lab
Can a sheet improve your sleep? Who can answer that? A dermatologist or sleep specialist with expertise in bedroom comfort? A product review blog or website? Or a series of tests simulating comfort sensations -- simulating how our bodies perceive comfort? Sheets.com is convinced it is the last of these.
Fabric Science: What is Comfort?
Comfort is a highly subjective perception. When you touch a fabric, the receptors in your skin are stimulated and the neural information is subjectively interpreted, in other words, it reflects your perception of multiple sensations.
Neurophysiology of sense perceptions. Hatch et all, 2000.
Over the years, large fabric manufacturers had to measure and predict their customers' perceptions of multiple sensations. Researchers developed methods to measure sensory perceptions objectively. In particular, Nike, Under Armour and other sports apparel giants developed tests in the 1980s to evaluate “fabric hand,” a term of art in the textile industry describing fabric quality and performance.
Just like these major fabric suppliers, Sheets.com applies precise, objective testing tools to evaluate sheets. We developed an easy-to-understand scoring system to measure and identify sheets that improve your sleep. No other retailer even comes close to performing this groundbreaking and meticulous analysis, conducted on more than 300 different sheets.
Once you know a sheet is evaluated, how do we find the rare few that truly improve sleep? First, Sheets.com identifies those with the highest score in each "Touch Descriptor" -- eight key terms that define the attributes of any fabric -- by using state-of-the-art testing instruments (see below). Then, we use proprietary AI to identify sheets that maintain lasting softness while offering varying levels of temperature and breathability to match how people experience comfort during sleep.
The Eight Touch Descriptors that Define the Attributes of Fabric:
| 1. Thermo-ception: | Cool | Warm |
| 2. Breathability: | Stuffy | Airy |
| 3. Texture: | Smooth | Uneven |
| 4. Body: | Delicate | Beefy |
| 5. Weight: | Heavy | Light |
| 6. Suppleness: | Crisp | Relaxed |
| 7. Friction: | Slippy | Grabby |
| 8. Elasticity: | Snug | Loose |
Objective test instruments can measure comfort perception!
With low forces applied, as when touching and manipulating fabrics, our RealFeel lab instruments use mechanical sensors to quantify each Touch Descriptor.
1. Thermo-ception
Temperature measurement is accomplished by inserting a precision-sized sheet sample between a heated surface and a cool water bath. Instruments measure the amount of power required to increase the water temperature a specified amount. Low power requirements means the sheet is conducting heat and will feel cooler to the touch. High power requirements mean the sheet is impeding the flow of heat and it will feel warmer.
2. Breathability
A sheet’s ability to diffuse moisture into the environment is measured by vapor transmission tests. The simplest tests utilize dishes of water that are covered by various sheet samples. Each is weighed and placed on a vibration-free turntable that rotates to ensure all dishes are exposed to the same average ambient temperature. The dishes are re-weighed in 24-hour intervals to calculate the rate of moisture vapor loss. Dishes that lose the most weight indicate greater diffusion of moisture vapor through the sheet.
3. Texture
Surface smoothness is evaluated by stretching a sheet and rolling a miniscule ball across the surface. A sensor measures the amplitude of the ball's movement as it rises to trace the contours of the yarn or falls into the gaps between yarns. Measurements of the distance between the ball’s upward and downward movements provide a separate wavelength image of the sheet’s surface.
To evaluate softness in both directions – top-to-bottom and side-to-side -- the sample is rotated 90° and retested. Because some sheet weaves (satin, knit for example) create different surfaces on the face and the reverse, the tests are repeated on the opposite side.
4. Body
Body is a combined measure of weight and thickness. The dimensions of a sheet sample are precisely measured. The sample is placed in a weighing dish that prevents the edges from unbalancing the measuring device. Multiple weight tests are conducted and the results are averaged.
As fabric absorbs water from the ambient atmosphere, the relative humidity and temperature are tightly controlled within an enclosed environment. Airflow is also eliminated during measurement.
Sensors are lowered onto a sheet swatch and force is applied. Thickness is measured under maximum compression for the sheet type and also at zero pressure. Changes in the thickness of the sheet are measured and the two measures are averaged.
5. Suppleness #1: Bending
The pliability of a sheet is evaluated in part by fabric-bending tests. The edges of a sample are mounted to the vertical instrument to eliminate the effects of gravity. One edge is held stationary while the other edge rotates forward and backward around a circular arc. Sensors measure the amount of force required to bend the fabric in both the forward and backward movements.
To measure a sheet’s ability to bend, top-to-bottom as well as side-to-side, the sample is rotated 90° and retested.
6. Suppleness #2 : Shearing
Shear tests complement fabric-bending tests in evaluating pliability. A sheet sample is clamped on opposing edges, which move in parallel and perpendicular directions. The stress in two simultaneous directions causes the sample to deform in an angular shape. The yarns slip and slide past each other in response to the angular forces. Sensors measure the ease or difficulty with which the yarns adapt to the angular stress. Sheets with higher thread counts or tighter weaves have more ‘locking’ intersections. The yarns are less able to adapt to the stress and feel generally less pliable.
7. Friction
Surface friction tests are conducted on a sheet sample that is stretched on a rack. A sensor rests upon the fabric surface and is pulled across it; the amount of force required measures the resistance of the sheet’s surface. Higher forces indicate a rougher fabric. The tests are repeated after the sample is rotated 90° to evaluate surface friction in both the top-to-bottom and side-to-side direction.
Sateen and knit constructions produce different surfaces on the face and the reverse of the sheet, so friction tests are repeated in both directions on the opposite surface. It is important to recognize which side is touching the skin because surface friction is very different from one side of those sheets to the other.
8. Elasticity
Strength and elasticity tests characterize the “give” of fabric under pressure. A sheet sample is clamped on opposing edges and force is applied as the clamps move apart. Sensors measure three fabric responses to the stretching force: 1) the maximum force before the yarns break and the sample bursts – tensile strength; 2) the percentage of stress at maximum force without bursting -- elasticity; 3) the percentage of recovery of the yarns when the applied force is removed -- resilience.
Strength and elasticity tests are conducted both in the top-to-bottom and side-to-side directions.
Correlation analyses of the three fabric responses provides a summary evaluation of the sheet. The factors that are included in the correlations are the i) number of yarns (thread count); ii) the size of the yarns (denier); iii) the fiber (i.e. cotton; polyester; microfiber polyester, silk, flax); iv) the quality of the fiber (for cotton: Supima; Pima: Egyptian; Upland) and v) the yarn quality (spinning wind-down; plies).