In our opinion, putting your door drop in an envelope is a trade-off.
When a leaflet not in an envelope lands on the doormat, it is there for the householder to see. They have to pick it up. At this point, your leaflet will be visible, and if it is of interest or relevant, they will not throw the leaflet away immediately. Still, they will either action it straight away or put it somewhere where they will see it again to action later.
If the leaflet is in a plain envelope, certainly a percentage of householders will open the envelope to see what’s inside. At this point, they will see the information on the envelope and then keep or discard the leaflet depending on the relevance as above. Some people, however, will discard the leaflet immediately without opening it because they will regard it straight away as letterbox spam.
There is some argument that with the Royal Mail, the envelope will benefit from being with post and therefore be opened. But will the considerable extra cost of enveloping generate enough additional enquiries to pay for it.
We have seen offerings in envelopes over the years, and often there is a paid reply card, so that could be some justification of the envelope. However, in today’s modern age, we think all that is needed is a high-quality leaflet with a freephone number and a website address. Don’t put the leaflets in an envelope and use the money saved to send out a higher number of leaflets.