Second spunbond polypropylene sock filter for under a couch or bed

This is the second of these I've built.  This one is about 181 cubic meters 

per hour CADR (107 cfm) and very quiet.

Step 1

Total time taken 40 min (including taking of photos along the way)

Take 4.8 meters of 1metre wide 80gsm spunbond 

polypropylene and fold that into thirds on a flat 

surface (now 1.6 meters long and three layers deep).  Put in a staple at each corner to stabilize the layering. Also one 80 cm down the length on each side.

Step 2

Fold that in half the other way (now 1.6m long by 0.5m and six layers deep)

Some more staples so it can't be opened out again.

Step 3

One more fold so you have 1.6 m x 25 cm:

Another staple through all the layers:

The run a line of those staples all the way down the 1.6 m length on that edge.

Step 4

Staples on end like so to make where you attach the fan:

Step 5

Close up the other end with staples.  You could make it flat, but I made mine triangular.

Step 6

Cover the open end with some duct tape and insert 

the coiled steel wire after stretching it 

out to be the right length and ensuring the ends 

are not sharp

Step 7

Tape the fan onto the SBPP.  Use short pieces of 

tape with the first couple being on the inside while you still can. The fan I used: https://www.quietpc.com/nf-a12x25-5v

Result

I say here that the speed is 2.7 m/s but a second attempt with a new battery and more carefully determined the average speed. Now I measured 5.5 average m/s for the open air-flow area (at the fan surface)  

In CADR calculator for these wee fans app  

Likely this is a 181.35 cubic meters per hour or 106.74 cubic feet per minute (cfm) delivery of clean air. You'd place it so that the air blown out can go some distance before hitting something solid so as not to create an entrapped/circular flow.

Lastly

I took the fan out, cut off the corners and put it back in again for a better inside-the-fabric fit. There was a chance that cutting the corners off would ruin the structural stability of the housing. That would have manifested itself as the fan hitting it's own housing or increased noise when running. Luckily that neither happened. I might make a change to a string tourniquet to hold the SBPP onto the fan housing as a next step.

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