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Functional Design Sweetie Pie Bag Expander Review

The Functional Design Sweetie Pie Bag Expander is a versatile, zip-in, sleeping bag expander that can be used singly for individuals that enjoy more space, or together with another expander as a sleeping bag doubler. Two expanders can also be zipped together to form a child-sized bag allowing for an adventurous toddler to have his own space.

Overall Rating: Average

The Bag Expander offers excellent versatility and design for families wanting to explore the wilderness. It is easy to use in most full-zip sleeping bags, and there's nothing on the market that compares. However, from an ultralight perspective, it's bulky and the materials are heavy.

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by Marty Coatney |

BackpackingLight Staff reviewed the Functional Designs Sweetie Pie Summer Bag Doubler in 2002. The Expander is half the size of the Doubler, with slightly different functionality.

Functional Design Sweetie Pie Bag Expander Review - 1
The Sweetie Pie bag expanders allow plenty of space for two adults and a toddler to sleep comfortably.


For a family backpacking with a toddler, the options for sleeping bag setups are very limited. Most sleeping bags available for smaller children are more suited for slumber parties than real outdoor pursuits. Enter the Sweetie Pie Bag Expander by Functional Design.

Functional Design Sweetie Pie Bag Expander Review - 2
Two Expanders zip together to form the equivalent of the Functional Designs Doubler.

The Expander zips into an existing sleeping bag. One Expander, by itself, widens the top of the bag by 28 inches, allowing for plenty of space for a parent and child to cuddle. By zipping two Expanders together, you get the equivalent of a Sweetie Pie Doubler, or almost 60 additional inches across the top of the sleeping bag. This allows enough room for two adults AND a toddler. The pair of Expanders can also be zipped together on both sides to make a toddler-sized sleeping bag.

Functional Design Sweetie Pie Bag Expander Review - 3
One Expander allows plenty of room for Mama and a wiggly two-year-old. Two Expanders create a sleeping bag just the right size for a child up to four feet tall.

We used two Sweetie Pie Expanders together with one bag on several family backpacking trips. The bag has plenty of space for all three of us to sleep comfortably, with even a little extra to move around some. (Disclaimer: Our son, Porter, has slept on my arm, by my side, since the day he was born. Others not used to a "family bed" may experience different results.) The two layers of Polarguard 3D in the three-season Expanders were warm enough for three-season usage, but almost too warm with all the extra body heat during summer trips. Luckily, the zipper options on the Sweetie Pie allow for venting at either feet or shoulders.

In breezy conditions, the Expanders are not quite as comfortable. They do not have a mechanism such as drawstring, Velcro, tonsil, or a draft tube to close of the top edge of the sleeping bag. Any wind that enters the tent enters the bag. In a tent that could be sealed to the ground on both ends, this problem could be somewhat mitigated, but drafts are a serious consideration for tarp and tarp tent users. This gap also makes it difficult to hold in heat.

My other issue with the design of the Sweetie Pie is the choice of materials. I wish there were an option for a down-insulated version or lighter weight fabrics. The overall purpose of the Sweetie Pie system is to leave a sleeping bag (or with a child, two) at home. Two Expanders and even a Doubler by itself weigh the same or more as many three-season down bags, and only compress to the size of a large sleeping bag. The use of down or lighter synthetics as insulation would solve both problems. That said, these materials would surely add to the quite reasonable $59.00 price of the Expander.

Overall, the Sweetie Pie Sleeping Bag Expander system is a great choice for keeping a family together in wilderness. With some updated, lighter weight materials to go along with the inventive, versatile design, Functional Designs would have a definite winner.


  • Manufacturer: Functional Design
  • Year/Model: 2007 Sweetie Pie Bag Expander
  • Materials: 50 denier ripstop nylon
  • Insulation: Polarguard 3D
  • Features: Draft tubes along zipper, double layer insulation with offset stitching, full-length 70" YKK #8 separating coil zipper
  • Weight: measured 18.7 oz (530 g), manufacturer specification 19 oz (539 g)
  • MSRP: $59.00 US each, or two for $99.00 US


"Functional Design Sweetie Pie Bag Expander Review," by Marty Coatney. (ISSN 1537-0364)., 2009-04-21 00:00:00-06.


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Functional Design Sweetie Pie Bag Expander Review
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Addie Bedford
(addiebedford) - MLife

Locale: Montana
Functional Design Sweetie Pie Bag Expander Review on 04/21/2009 17:09:19 MDT Print View

Companion forum thread to:

Functional Design Sweetie Pie Bag Expander Review

Jeremy Greene
(tippymcstagger) - F

Locale: North Texas
strange timing of this review on 04/21/2009 17:58:31 MDT Print View

They are selling off their inventory at 1/2 price and discontinuing production. I don't think I could get materials for that price.

We've been fairly happy with a similar homemade item. We made it from a retired summer bag. With the (larger) mummy on top I don't notice a draft at the zipper. As for the draft between partners, there has been plenty of discussion on this site.

tracey byrne
(tabseattle) - F
close out sale info from Functional Design on 04/22/2009 11:39:29 MDT Print View

Hello all,
it's true, we are having a close-out sale, and you can purchase the Doubler for $49 or Expander for $39, for as long as our inventory lasts.
We are discontinuing this patented product due to changes in the YKK zipper; we're unable to keep up with all the variations, and there is no longer a "standard". Be sure to check our website for a list of compatible sleeping bags.
A note for those looking for a light-weight option: our summer Doubler weighs only 19 oz.