Here's a short explanation from the gore-tex website:
- 2-layer construction: a specific GORE-TEX® membrane is laminated to the inside of the outer material. The inside of the membrane is protected by a separate lining- - 2-layer insulated construction: the heat-insulation layer is is suspended freely between the 2-layer laminate and inside lining
- - 3-layer construction: a specific high-performance GORE-TEX® membrane bonded to a tough outer material and a specially developed robust inner lining
And here's some more info from the Sweet Protection pages.
3-LAYER vs. 2-LAYER GORE-TEX® GARMENTS
All GORE-TEX® outerwear comes in two different constructions; 3-layer and 2-layer. Both provide reliable and effective protection against the elements; totally waterproof, totally windproof and highly breathable. Special Gore-seam® tape technology ensures all seams are 100% waterproof. Here’s a quick look at the differences between the two constructions:
3-layer GORE-TEX® garments
In the 3-layer design, the GORE-TEX® membrane is bonded to the (inside) lining on one side, and to a breathable and abrasion resistant outer fabric on the other (outside). The result is a sandwich of three fabrics, hence the name 3-layer construction, bonded together in a single, tough layer.
Benefits: 3-layer GORE-TEX® fabric’s sandwich-style construction provides enhanced breathability and durability. It’s the favorite among advanced users, and used in our top of the line clothing. It’s also lighter than 2-layer GORE-TEX® fabric, since it requires no additional free-hanging liner.
Considerations: The 3-layer construction is slightly stiffer and less subtle than 2-layer. It normally feels a little “crunchier”
2-layer GORE-TEX ® garments
In the 2-layer construction, the GORE-TEX® membrane is bonded to a breathable and abrasion resistant outer fabric. The lining remains loose and is there to protect the GORE-TEX® membrane from abrasion.
Benefits: 2-layer garments are warmer, softer and with a more comfortable feel. On 2-layer garments it’s also easier to implement more details.
Considerations: 2-layer GORE-TEX® garments will normally have a higher RET (evaporative resistance of a textile) value. (Lower RET = better breathability). 2-layer garments are also slightly heavier than 3-layer garments.
Although both all of this is specifically Gore-Tex related, the principles are the same for other manufacturers..
