Comfort characteristics of Knitted Microfiber Fabrics

Now a days, garment physiology, environmental behavior, comfort and lifestyle have become an important part of modern fabric making. Garments that light up, garments against stress, garments with ultraviolet ray blockers and garments with air conditioning.... all these are not imaginary aspects, but facts.

In the first half of the 20th century active wear was not designed systematically, as less suitable natural and man-made fibers were available. But in the recent times, it has all become possible with microfibers.

The microfiber yarns show filaments and staple yarns of acrylic polyamide polyester and polyolefin, the individual filaments of which are finer than 0.9 deniers but are normally put around 0.5-0.7 deniers, which are considered as super microfibers. Because of superior breathability and moisture transport properties, wind and waterproofness, these fabrics are extensively utilized in rainwear and active sportswear.

While we frequently use the expressions "textile comfort" and "clothing comfort", what they really signify is the comfort of the wearer on utilization of a certain clothing or textile item. Both physiological, as well as psychological aspects are applicable to comfort. Our body produces moisture in the form of perspiration. There are mainly two types of perspirations: sensible perspiration and insensible perspiration. Sensible perspiration is liquid perspiration formed under hot and/or active situations and insensible perspiration evaporates within the skin layers and is released as water vapor.

As long as perspiration is insensible (i.e. in the form of vapor), the body feels quite comfortable. But when this vapor cannot evaporate, a vapor pressure is created near the body and the RH at the skin raises. The body experiences clamminess and then this vapor may condense to liquid moisture or sweat raising discomfort. As RH increases, the pace of evaporation decreases. Under such circumstances, the contribution of textile fabrics to comfort depends on their capability to take away the water vapor or to maximize the evaporation of any liquid moisture.

Under strenuous activity, the body tries to adjust its temperature by giving off heat. This equilibrium between heat production and heat loss is actually what we connote by 'comfort'.

For Indian geographical surroundings, where perspiration dissipation is an important aspect of all comfort garments, it is essential to understand the factors implicated in designing a material for sportswear that will be breathable and comfortable.

Methods and material
In a study conducted, three types of fabrics were taken as samples:
1.Polyester microfiber (PM) double jersey knitted fabric.
2.Polyester nonmicrofiber (PN) double jersey knitted fabric.
3.Polyester microfiber cotton interlocks reversible fabric (PM/C) with polyester microfiber on one face and cotton on the other face of the fabric.

The preliminary data of the fabric has been given in Table I.

The assessment for all the above three fabrics was done in three phases. Phase-I of the study covered analysis of the fabrics for comfort properties, like wicking behavior, air permeability and tightness factor.
Phase-2 of the study covered the fabrication of instrument for perspiration absorption and a study on it for assessing the comfort. Phase-3 covered formulating the interview schedule and the wear trials.

Phase - I
Wicking behavior

Through the vertical wicking strip test, the wicking behavior of all the samples was evaluated.

Air permeability
For calculating air permeability the fabrics were examined on the Air Flow Tester model No 9025 (US Testing Co Inc, Hoboken, N J). The survey of air permeability was done from the calibrating table equating pressure drop to the rate of airflow.

Tightness factor
Tightness factor is the ratio of the area covered by the yarn in one loop to the area enclosed by that loop. Tightness factor (K) was derived by the formula:Where, T = yarn linear density in tex and L = Stitch length in mm.

An instrument was designed which assessed the fabrics as to how they would react when rubbed against a sweating skin (Plate-I). For this reason, a rectangular steel container of 6 inches x 8 inches x 4 inches dimensions was placed. A geyser heating component was put on the inner side of the container so that water could be heated inside the container. In order to maintain the temperature at the boiling point, a thermostat was attached with the component.

A cross grid was put on the face of the container, which covered it completely. On the grid a thin synthetic sheath was placed. This sheath was obtained from the upper dry weave covering of whisper sanitary napkin. This specific sheath was chosen for two reasons, firstly because it simulated the human skin with pores, and secondly it was robust to hold up the rubbing action against the fabric.

The entire assemblage was put inside a water bath shaker. Only the water bath shaker was utilized to keep a constant movement of the 'skin assembly'. The whole assemblage was put on the stand of the water bath shaker. Through wires, a wooden frame was connected only to the water bath and not to the shaker platform. The wooden frame had two iron strips at two ends for holding the fabric sample. As a result, the fabric was kept in one fixed position on the top while the whole skin assembly actuated against it causing 'sweating' and 'sweat absorption'.

The samples were tested under two conditions - with fan and without fan, i.e., with air movement on the fabric and without any air movement on the fabric. For the air movement, a portable fan was placed exactly above the 'skin assembly'. The speed of the fan was kept constant. For testing in the 'no-air condition', the fan was detached from the assembly.

For analyzing, the conditioned samples were weighed. A container filled with water was kept for heating electrically. The grid was affixed with the sheath. In the meantime, the sample was shaped up on the frame. Once the vapor started forming, the shaker was set in motion. The fabric rubbed against the sheath and the grid. This process continued for 15 minutes, after which the sample was removed and was weighed without any delay.

The per cent absorption was then derived by the formula:

Phase - III
This phase consisted of making T-shirts, wear trial and examination through the interview schedule. T-shirts were made from each fabric. The designed T-shirts were with full sleeves and a closed round neckline. This model was selected so that no sweat could getaway from the torso of the wearer and maximum sweat could be trapped in the T-shirt.
For the wear trials, three subjects were selected and prepared to wear the pre-weighed, conditioned T-shirts and were made to work out on the treadmill for 15 minutes. The T-shirts were then taken back and were weighed instantly to determine the sweat absorption percentage. The wear trials were also carried out under two conditions - with and without fan.

After each wear trial, each subject was provided with an interview schedule comprising of questions associated with demographic data, body weight and eating habits. Certain adjectives like hot, clammy, breathable, raggy, steamy, soft, sticky, etc. were also provided, which made them easier in clarifying how they felt while wearing the garment and carrying out the wear trial. Moreover, they were asked for their feedback and a 5-point comfort rating scale was used to evaluate the comfort level.

Results and discussion

Phase - I
i) Wicking behavior

It was noted that the course-wise samples wicked more than the wale-wise samples in the wicking strip test. The highest absorption was observed in PM fabric, followed by PN fabric, and the least absorption was observed in PM/C fabric (Table 2). The PN and PM fabric wicked in no time but the PM/C sample took the maximum time to wick entirely. This may initially be characterized by the textured property of synthetic fibers in PM and PN fabrics. The sum of textured yarn existing in the PM/C fabric is little and therefore the percentage absorption of the fabric is also small. In the PM/C fabric, the microfiber side wicked rapidly, but the cotton side in turn absorbed water from the adjacent microfiber layer, so the absorption was uneven and patchy.

ii) Air permeability

The maximum airflow was observed in PN fabric followed by PM fabric and then by PM/C fabric (Table 3). The maximum air permeability of PN fabric may be characterized by its loose knit structure. The PM fabric was more compressed than the PN fabric. In the case of PM/C fabric, the lowest air permeability may be characterized by its double knit structure, compactness of the knit and also the thickness of the fabric.

iii) Tightness factor

The tightness factor was highest for PM/C reversible fabric followed by PM and then PN fabric. This can be characterized by the loose knit of PN fabric and the compactness of PM/C reversible fabric (Table 4).

Relation between air permeability and thickness depicted that, as the thickness of fabric increases, the airflow decreases. The relation between the tightness factor and air permeability showed that as tightness factor of a fabric increases, the airflow through the fabric decreases.

Outcome related to testing on the fabricated instrument for perspiration absorptions to test comfort.

It was noted that while testing, more absorption occurred in the course-wise samples than in wale wise samples (Table 5). The highest absorption in 'no-air' condition was observed in PM (course wise) followed by PN (wale wise) samples. While testing with fan, the best moisture transport properties were shown by the PM fabric followed by PN and then the PM/C fabric.

Phase - III
The wear trials were conducted under two settings - with and without fan. It was noted that in both the settings, the PM fabric T-shirt showed the best absorption and moisture transport properties followed by PN fabric T-shirt. The PM/C fabric T-shirt performed the least absorption and moisture transport properties (Table 6).

On evaluating the amount of absorption by the test fabrics during the wicking test, testing on the fabricated instrument and during the wear trials, it was noted that though the amount of absorption during all the three tests was unalike, the comparative pattern of absorption for all the three fabrics during all the three tests was observed alike (Table 7).

The PM fabric absorbed the most followed by PN fabric. The least absorption was observed in the PM/C reversible fabric. The variation in the amount of absorption may be because of many reasons, some of them being the size and weight of the samples, the atmospheric conditions and the occurrence of absorptions in the three tests.

In the wicking test, the absorption occurred because of capillary forces, which went against the force of gravity, but absorption in the fabricated instrument occurred as a result of water vapor and the rubbing action of the sample against the sheath covered grid. The same was observed in the wear trials where the environmental factors, the rate of sweating and the friction between the fabric and the skin caused the absorption.

Comfort rating scale
To examine the discernment of comfort by the subjects about the T-shirts, a 5point comfort rating scale was formulated.
.Extremely comfortable -5
.Comfortable -4
.Mildly comfortable -3
.Uncomfortable -2
.Extremely uncomfortable -I
Each subject was asked to rank the garment with regards to this scale. Points were then given to each rating. In order to see which T-shirt ranked at the top most position, the points of the three T-shirts were added for both the conditions.

The final result (Table 8) of the comfort rating scale used indicate that all the subjects rated the PM T-shirt as the most comfortable, with a total rating of 13 with fan and 12 without the ventilated condition. The second best rating, 12, was provided to the PN T-shirt with fan, which was equal to that of the PM T-shirt under non-ventilated conditions. This ranking was followed by that of PN in no-air condition which was 10.

Conclusively, the PM/C T-shirt was ranked as the most uncomfortable in the comfort rating scale with 8 and 6 points in with air and with no air condition respectively. While rating the PM/C T-shirt, the subjects even stated that the T-shirt was not uncomfortable due to its fiber composition but the reality being that the T-shirt was very thick and it was getting uncomfortable due to the sensible perspiration, which did not have any outlet from the skin surface.

In case of ventilated settings for PN and PM T-shirts, the outcomes were outstanding and the ratings suggested that during testing trials for both T-shirts, the wearers felt relatively more comfortable than where there was no air circulation in the room.

The subjects also recommended that the PM/C fabric T-shirt would be more appropriate for sports in winters where the temperature is relatively cooler.

Perspiration dissipates quickly through evaporation from an unclothed body due to its direct contact with the surrounding atmosphere. While for clothed body, the perspiration is first absorbed by the clothing and for any fiber, may it be cotton or microfiber; it needs movement of air which acts as a medium for perspiration of dissipation.

While exercising, the body is at a higher temperature as compared to the clothing worn or the surrounding environment. So, rapid evaporation occurs and the vapor is absorbed by the clothing in the form of sweat.

Therefore, we find the T-shirts cool initially. But when the clothing is at a lower temperature and further transport of perspiration to the outside surroundings is hindered, the ventilated conditions play a significant part in carrying the sweat vapors from clothing to the nearby atmosphere.

Hence, it can be determined that textured pure polyester fabric is appropriate for wearing purpose under ventilated conditions. The total absorption on weight of the PM fabric may be less than PN when wear trial was conducted without fan but under high activity condition with fan, the PM fabric retains more sweat than the PN fabric.

Minimum absorption is observed in PM/C reversible fabric. The main disadvantage of the PM/C reversible fabric is that it is extremely thick. Even though the weight of the fabric before and after the wear trials is more than the other two fabrics, the percentage absorption 0wf is relatively less, which shows higher absorption properties of PM and textured PN against PM/C.

Here the bulk of textured yarn plays a significant role. Both textured fabrics - PM and PN, illustrate high percentage absorption. The more the bulk more will be the absorption and retention of sweat. In spite of having the microfiber property of being breathable with rapid sweat dissipation, the PM fabric T-shirt depicts less percentage absorption as compared to the PN fabric T-shirt. But more significant than this is the property of texturing after which the kind of fiber doesn't matter. Any fiber can be made comfortably by texturing it. Cotton fiber has its natural waviness, but it is unmatched to those of synthetic fibers.