|Full-length Therm-a-Rest Z-Lite|
Depending on the pad, the weight difference between 3/4-length and full-length can be anywhere from 4 to 5 ounces (for ultralight pads like the classic Therm-a-Rest RidgeRest or high-end NeoAir XLite) to as much as 8 ounces or more for heavier versions like the inexpensive Trail Scout. 3/4-length pads also pack down smaller than their larger brethren, a boon for smaller packs.
I've used both lengths over the years. Here's my personal take on the two options.
First, I've found there to be no meaningful difference in sleeping comfort between the two.
The most important places to have padding for a good night's sleep are beneath your shoulders, hips, and knees. Even for a tall guy like me (6 feet, 5 inches), a 3/4-length pad provides sufficient knees-to-shoulder coverage. You don't need a pad under your head, since you'll be using some sort of other padding for a pillow (here's my recommended pillow solution); or under your ankles and feet, which don't create much in the way of pressure points.
There's one important caveat to this, however. I have noticed that thick 3/4-length pads (2 inches or more) create a distinct drop off below the knees that is uncomfortable. For me, this often results in sleeping discomfort and noticeable soreness in my knees the next day. Consequently, I generally don't recommend thick 3/4-length pads. If you want that amount of cush, go for the full-length.
Second, 3/4-length pads require that you put something else under the tail of your sleeping bag.
You don't want the end of your sleeping bag lying directly against your tent floor or, worse, against a shelter floor or directly on the ground if you're sleeping outside. Doing so exposes your sleeping bag to moisture, dirt, and abrasion.
It's an easy problem to deal with—you can place a garbage bag or lightweight tarp or ground sheet beneath your feet, or use your pack or rain gear if you want to go minimalist—but it does require a small amount of hassle.
Third, I personally use a full-length ultralight pad.
I continue to use a full-length Z Lite pad (pictured above), which has been my go-to three-season pad for nearly two decades. For me, the extra 4 ounces and coverage of a full-length vs. 3/4-length version is well worth the small additional weight.
I will grant, however, that the thin padding of the Z Lite is not for everybody. If you need a thicker, cushier pad for a good night's sleep that doesn't leave you feeling like a sore and creaky Tin Man the next morning, the weight and bulk differences between a 3/4 and full-length pad become more striking—and require more careful consideration.
“Equipped” is an AMC Outdoors blog, written by Matt Heid.