3.1 Subjective Comfort Evaluation Results
Tables 2 and 3 show the results of the subjective comfort assessment for pillows with different heights (Fig. 3).
Pillow’s subjective comfort evaluation results show that the subjects like 7 cm high Pillow 2 most, which was followed by 3 cm high Pillow 1.
3.2 Body Pressure Test Results Under Different Pillow Heights
All the standardized values in the tables are percentages, i.e., the percentage values standardized based on the maximum value of each subject. Tables 4, 5, 6, 7 and 8 show the results of body pressure distribution test under different pillow heights.
With the increase in pillow height, F neck and F waist increased while F chest decreased progressively.
With the increase in pillow height, PF neck and PF buttock had an increasing trend while PF head had a decreasing trend. With pillow height less than 3 cm, the body’s peak pressure appeared in the head; when the pillow was higher than 7 cm, the body’s peak pressure appears in the buttocks.
In the supine lying position, the maximum body’s pressure intensity appeared in the buttock area; the increase in pillow height, CP neck increased.
With the increase in pillow height, PCP neck increased, PCP head had decrease trend and PCP buttock and PCP shank-foot had increase trend. When the pillow height was less than 3 cm, the peak pressure intensity appeared in the head; when the pillow was higher than 7 cm, the peak pressure intensity appeared in the buttock and shank-foot areas.
With the increase in pillow height, CA neck increased while CA chest decreased.
3.3 Statistical Analysis Results
3.3.1 Pillow Height and Comfort
Table 9 shows the analysis results of correlation between pillow height and subjective comfort evaluation.
According to the results of Spearman rank correlation analysis, the correlation coefficient between pillow height and shoulder comfort was the highest, i.e. −0.517, which was followed by head and neck comfort, and the correlation coefficient was −0.494.
3.3.2 Most Comfortable Pillow Height and Body Measurements
Table 10 shows the analysis results of correlation between the most comfortable pillow height and the body size.
As shown by the correlation analysis results, the most comfortable pillow height and shoulder width was most relevant, in which the shoulder width had correlation coefficient of 0.463 and the correlation coefficient with shoulder width was 0.523.
3.3.3 Difference in Body Pressure Distributions Under Different Pillow Heights
Differences in body pressure distributions under pillow heights of 0 cm, 3 cm, 7 cm, 11 cm and 15 cm were compared with the use of one-way anova, LSD (homogeneity of variance) and Dunnett T3 (heterogeneity of variance) follow-up inspection.
The significance indicators of one-way anova were F neck, CA neck, CP neck, CP chest, PF head, PF neck, PCP head and PCP neck (Tables 11, 12, 13, 14 and 15).
The results showed that the pillow height had a significant effect on change in subjects’ neck pressure, and the neck pressure increased while the chest pressure had decrease trend with the increase in pillow height.
The pillow height had a significant effect on the peak pressure of neck, and the peak pressure of head had a decrease trend with the increase in peak pressure of neck.
‘With the increase in pillow height, the neck pressure intensity had an increase trend.
When the pillow was higher than 7 cm, the head peak pressure decreased significantly; relative to absence of pillow, the peak neck pressure intensity with pillow increased significantly, and with the increase in pillow height; with pillow height of 11 cm, the peak pressure intensity of buttocks was the highest; the peak pressure intensity of shanks and feet was the highest without pillow.
The head contact area and the chest contact area were highest at the pillow height of 3 cm. Buttock contact area reached the maximum at the pillow height of 7 cm. Neck, waist and thigh contact areas had the trend to increase with increasing pillow height. Relative to the absence of pillow, the use of pillow allows a significant increase in neck contact area.