The impact of sleepwear fiber type on sleep quality under warm ambient conditions

Figures & data

Table 1 Fabric characteristics of washed sleepwear

	Mass per unit area (g·m^−2)	Thickness (mm)	Thermal Resistance (m^2·K·W^−1)
Cotton	140.0±0.0	0.57±0.03	0.030
Polyester	150.5±0.7	0.49±0.04	0.025
Wool	143.5±2.1	0.52±0.01	0.030

Note: Data presented as mean ± SD.

Table 2 Effect on sleep parameters of sleepwear fiber type

	Cotton	Polyester	Wool	p-value
SOL (min)	18.5±23.5	18.2±15.5	16.0±15.5	0.04
REM sleep latency (min)	82.5±34.2	88.9±46.7	82.6±49.0	0.33
N1 (%)	5.3±4.0	4.6±2.5	4.6±2.7	0.57
N2 (%)	58.6±9.0	57.5±8.6	57.8±8.0	0.70
N3 (%)	15.9±5.4	16.1±6.8	16.5±5.7	0.91
REM sleep (%)	20.2±5.7	21.5±6.3	21.1±6.1	0.58
TST (min)	363.4±56.0	364.2±62.6	373.1±60.4	0.30
SE (%)	76.2±11.0	76.4±12.4	78.4±12.6	0.32
WASO (min)	97.0±52.3	95.8±56.6	89.1±57.0	0.76
AI (no.h^−1)	10.3±7.1	9.6±6.0	10.5±6.4	0.36
SFI (no. h^−1)	13.3±5.8	13.7±4.4*	12.1±4.2*	0.01

Notes: Data presented as mean ± SD, N=36. *p<0.05 for difference between polyester and wool.

Bold values indicate significant sleepwear effect on SOL but there was no significant difference among sleepwear types in the post-hoc pairwise comparisons.

Abbreviations: SOL, sleep onset latency; REM, rapid eye movement; TST, total sleep time; N1(%), sleep stage 1 as a percentage of TST; N2(%), sleep stage 2 as a percentage of TST; N3(%), sleep stage 3 as a percentage of TST; SE, sleep efficiency; WASO, wake after sleep onset; AI, arousal index; SFI, sleep fragmentation index.

Table 3 Effect on sleep parameters of sleepwear fiber type for subgroup BMI, Age and PSQI

	BMI<25 (n=13)	BMI≥25 (n=23)	p-value	Middle-age (n=23)	Old age (n=13)	p-value	PSQI<5 (n=20)	PSQI≥5 (n=16)	p-value
SOL (min)	17.8±26.1	17.5±12.4	0.14	16.1±12.9	20.2±25.4	0.03	11.0±7.0	25.8±24.2	0.17
REM sleep latency (min)	83.3±36.9	85.4±47.0	0.84	86.4±46.5	81.6±38.0	0.92	71.1±33.7	101.6±48.5	0.07
N1 (%)	3.3±1.8	5.7±3.4	0.03	4.5±3.0	5.5±3.2	0.42	4.9±2.9	4.8±3.4	0.84
N2 (%)	57.8±8.1	58.1±8.7	0.35	59.1±8.1	56.0±8.8	0.05	56.0±8.2	60.5±8.2	0.01
N3 (%)	18.2±7.0	15.0±5.0	0.02	15.8±5.9	16.8±6.0	0.03	16.3±6.1	16.0±5.8	0.12
REM sleep (%)	20.7±4.8	21.1±6.6	0.87	20.6±6.2	21.4±5.7	0.87	22.7±5.4	18.8±6.1	0.05
TST (min)	381.7±62.6	358.6±56.1	0.31	364.4±63.6	371.3±51.4	0.71	379.4±46.1	351.4±70.0	0.56
SE (%)	78.2±10.4	76.3±12.7	0.88	77.2±13.5	76.6±8.7	0.15	81.0±9.7	71.9±12.6	0.23
WASO (min)	88.1±43.9	97.3±60.4	0.89	95.3±63.3	91.6±36.4	0.42	79.3±46.3	112.3±59.6	0.37
AI (no./h)	6.8±2.9	12.1±7.1	0.04	9.3±7.1	11.6±5.0	0.32	9.2±4.9	11.3±7.9	0.55
SFI (no./h)	11.2±2.8	14.1±5.5	0.09	12.2±5.0	14.6±4.2	0.32	11.4±3.8	15.1±5.2	0.01

Notes: Data presented as mean ± SD.

Bold values indicate significant BMI, Age and PSQI effect on sleep variables. 

Abbreviations: BMI, body mass index; PSQI, Pittsburgh Sleep Quality Index; SOL, sleep onset latency; REM, rapid eye movement; TST, total sleep time; N1(%), sleep stage 1 as a percentage of TST; N2(%), sleep stage 2 as a percentage of TST; N3(%), sleep stage 3 as a percentage of TST; SE, sleep efficiency; WASO, wake after sleep onset; AI, arousal index; SFI, sleep fragmentation index.

Figure 1 Interaction effects between sleepwear and Age/PSQI on sleep variables.

Notes: (A) Sleep onset latency, between sleepwear and Age; (B) Wake after sleep onset, between sleepwear and PSQI; (C) REM sleep latency, between sleepwear and PSQI. Error bars with standard deviations are displayed. Comparison between sleepwear conditions indicated by *p<0.05 between cotton and wool; †p<0.05 between polyester and wool; ±p<0.05 between cotton and polyester; α, p<0.05 between groups.
Abbreviations: PSQI, Pittsburgh Sleep Quality Index; REM, rapid eye movement.

Figure 2 Estimated whole body sweat evaporation rate (WBSER) (g·h⁻¹).

Notes: Error bars with standard deviations are displayed. The equation used for the calculation of WBSER can be found in the section Data and Statistical Analysis.

Table 4 Subjective ratings on tactile sensation for each sleepwear

		Cotton	Polyester	Wool	p-value
Surface texture	After donning	2.08±0.73	1.75±0.73	2.22±0.96	0.065
	At bedtime	2.19±0.62	1.81±0.75	2.28±0.94†	0.037
	On waking	2.36±0.80	1.94±0.79†‡	2.36±0.87	0.045
Prickliness	After donning	1.17±0.45	1.17±0.45	1.64±0.90*†	0.002
	At bedtime	1.28±0.57	1.28±0.62	1.64±0.83*†	0.024
	On waking	1.33±0.76	1.36±0.68	1.72±0.85*†	0.022
Clamminess	After donning	1.13±0.48	1.19±0.62	1.16±0.56	0.912
	At bedtime	1.28±0.66	1.44±0.84	1.22±0.54	0.454
	On waking	1.42±0.77	1.64±0.83	1.53±0.81	0.339
Clinginess	After donning	1.11±0.40‡*	1.36±0.64	1.36±0.59	0.043
	At bedtime	1.19±0.47	1.42±0.84	1.44±0.65	0.182
	On waking	1.42±0.73	1.67±0.96	1.61±0.96	0.456

Notes: Data presented as mean ± SD, N=36. Tactile sensations included surface texture (1=“very soft” to 5=“very rough”), prickliness, clamminess and clinginess of the sleepwear (1=“not at all” to 5=“extremely”) and were assessed on a five-point Likert scale. Bold values indicate significant sleepwear effect on subjective ratings.*p<0.05 for difference between cotton and wool; †p<0.05 for difference between polyester and wool; ^‡p<0.05 for difference between cotton and polyester.