SFI 3.3. The NEW Simpson Pro-Fit Base Layers are our most comfortable and best fitting base layers. Constructed in Italy using the latest techniques, the Pro-Fit provides superior softness and stretchability. The trusted Nomex® material gives you an added layer of protection while maintaining breathability and comfort. Sizes range from XS-3XL. Color Options: True White and Carbon Black. Try our Long Sleeve Tops, Pants, and Balaclava Today!