The second aim of this study was to examine the validity of the newly-developed NIR (Futrex
®6100/XL) employing six wavelengths to estimate %fat. In 1984, Conway et al. [
10] measured infrared wavelengths from 700 to 1100 nm and determined that the peak absorption of pure fat occurred at 930 nm and pure water at 970 nm. Based on this research, the Futrex
®5000 utilized infrared wavelengths at 940 and 950 nm to measure optical density. The updated model of the Futrex
® (6100/XL) NIR device used in the current investigation employs six different wavelengths at 810, 910, 932, 944, 976, and 1023 nm to estimate %fat [
38]. The Futrex
®6100/XL has advantages over previous models because the wavelengths encompass the same range as in the original research by Conway et al. [
10] (700–1100 nm). Results from the current study indicated no difference between NIR and the 3C model for %fat estimations and produced acceptable
SEE (2.7%fat) and
TE (2.7%fat) values, as well as a good validity coefficient (
r = 0.82). Though other studies have validated earlier models (Futrex
®5000 and Futrex
®1000) in females compared to HW [
11,
12,
14,
15]; to our knowledge this is the first complete study to compare the new NIR device to any criterion method. However, previous studies concluded that neither the Futrex
®1000 or Futrex
®5000 were acceptable methods for estimating %fat with reported
TE values > 4%fat [
11,
12,
14]. Stout et al. [
15] was the only investigation that found acceptable agreement between the Futrex
®5000 and HW in women 17 to 29 years of age (20.1 ± 2.3 years). Nonetheless, Stout et al. [
15] concluded that, even though the
TE value of 3.9%fat is considered acceptable for the gross estimation of body fat, the Futrex
®5000 substantially condensed the distribution of body fat and constantly overestimated %fat. In agreement with Stout et al. [
15], the current investigation produced an acceptable
TE value (
TE = 2.7%fat). However, contrary to the conclusions of Stout et al. [
15] and the Futrex
®5000, the Futrex
®6100/XL appears to be a favorable device for measuring %fat in college women and can be considered a valid field method for estimating %fat in this population. Additionally, the validity coefficient (
r = 0.82) using the Futrex
®6100/XL is the highest reported of any prior research or Futrex
® model (
r < 0.63) [
11,
12,
14,
15].). It appears that the six wavelengths utilized in the Futrex
®6100/XL compared to the two wavelengths for the Futrex
®5000 and Futrex
®1000 improved the accuracy for estimating %fat in this population. Based on the current findings, the Futrex
®6100/XL appears to be a valid method for estimating %fat in college-age women; however, more research is required to validate our results. Additionally, the 95% limits of agreement suggest that NIR may over-predict %fat by as much as 4.2%fat and under-predict by as much as 6.2%fat. These individual variations are most likely due to the use of a single site measurement. Therefore, caution should be used when relying on NIR as a method to identify %fat in small groups or individuals. Future research should examine the validity of the Futrex
®6100/XL in different populations that include various races, sex, ages, degrees of fatness, and include multiple measurements sites.