Most folders are sized to hold standard 8.5" × 11" (letter) paper. Some envelope-style or larger holders list dimensions around 9.75" × 13" (about 10" × 13").
Display-style portfolios typically use top-loading clear sheet protectors and crystal-clear polypropylene sleeves that are archival-quality, non-glare, and waterproof so pages are visible while staying protected.
Dimensions vary by model. Examples from listings include 11.5" × 9.69", 10" × 13" × 0.7", 15.5" × 10.6", and about 13" × 9.75".
Many folders emphasize protection and durability: archival-quality, acid-free, non-glare, waterproof polypropylene sleeves; thick, sturdy covers; durable plastic exteriors; reinforced gussets; and tear-resistant materials.